St. Patrick’s Day Chocolate Cake With Green Buttercream

1 h 5 min | intermediate | vegetarian

Two-layer chocolate cake on a plate, frosted with thick swirls of pale green buttercream; a large wedge is cut out to show dark, moist crumb and a thin green frosting layer between the tiers.

Published Jan 10, 2026

Prep Time	Cook Time	Total Time
35 min	30 min	1 h 5 min

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Introduction

This St. Patrick’s Day chocolate cake is ultra moist, deeply chocolaty, and topped with a silky green buttercream frosting.

A hint of peppermint in the fluffy buttercream makes every bite taste like a festive chocolate mint treat.

It’s the perfect make-ahead dessert for St. Patrick’s Day parties, office celebrations, or a fun family dinner at home.

Close-up of a slice of two-layer chocolate cake on a white plate, filled and topped with pale green buttercream; a blurred cut cake sits in the background on a light marble surface.

How to Make St. Patrick’s Day Chocolate Cake With Green Buttercream

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Prep the pans and oven

Heat your oven to 350°F and grease two 8-inch round cake pans, then line the bottoms with parchment.
Combine the dry ingredients

Whisk the flour, cocoa powder, baking powder, baking soda, salt, and granulated sugar in a large mixing bowl.

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Mix in the eggs and oil

Add the eggs and vegetable oil to the dry mixture and whisk until the batter looks thick and slightly glossy.
Add the buttermilk

Pour in the buttermilk and vanilla extract, then whisk until the batter is smooth and no dry streaks remain.
Blend in the hot coffee

Slowly pour the hot coffee into the batter while whisking, which helps the cocoa bloom and deepens the chocolate flavor. The batter will look thin, which is exactly what you want for a very moist cake.

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Bake the cake layers

Divide the batter evenly between the prepared pans and tap them gently on the counter to release bubbles. Bake for 28 to 32 minutes, or until a toothpick comes out with just a few moist crumbs.
Cool the cakes completely

Let the cakes cool in the pans for 10 minutes, then turn them out onto a wire rack. Cool the layers completely before frosting so the buttercream does not melt or slide off.
Beat the butter for frosting

In a large bowl, beat the softened butter with a mixer on medium speed until very light and creamy.

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Add sugar, cream, and flavorings

Add the powdered sugar one cup at a time, mixing on low speed until combined and scraping the bowl as needed. Beat in the heavy cream or milk, vanilla, peppermint extract, and a pinch of salt until the frosting feels fluffy.
Tint the buttercream green

Add green gel food coloring a little at a time, beating after each addition until you reach your desired shade. If the frosting seems too thick, mix in a tiny splash of cream; if too thin, add more sugar.
Assemble and decorate the cake

Place one cake layer on a serving plate and spread a generous layer of frosting over the top. Set the second layer on top, then frost the sides and top, swirling or piping as festively as you like. Add sprinkles or chocolate shavings if you want extra texture and a fun St. Patrick's Day look.

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Substitutions

Replace buttermilk with milk and lemon juice or vinegar: Use 1 cup whole milk mixed with 1 tablespoon lemon juice or vinegar, then rest 5 minutes before using. This gives similar tang and tenderness, keeping the crumb soft and flavorful without needing store-bought buttermilk.
Replace hot coffee with hot stout beer: Swap the ¾ cup hot coffee for ¾ cup gently heated stout, like Guinness, for an extra Irish twist. The beer deepens the chocolate flavor and adds a subtle malty note while keeping the cake just as moist.
Replace green gel food coloring with matcha powder: Stir 1 to 2 teaspoons culinary matcha into the frosting for a natural green tint and gentle tea flavor. The matcha keeps the St. Patrick's Day color while adding a slightly earthy note that complements the chocolate.

Tips

Measure flour and cocoa carefully: Spoon flour and cocoa into your measuring cups, then level with a knife for accurate amounts. Too much of either makes the cake dense instead of tender and moist.
Use room-temperature ingredients: Room-temperature eggs and buttermilk blend more easily, giving a smoother batter and helping the cake rise evenly. Set them out about 30 minutes before you start mixing.
Level or trim domed layers: If your cake layers dome, gently trim the tops with a serrated knife once they are fully cool. You will get a stable, even stacked cake that is easier to frost neatly.
Chill the crumb coat: Spread a thin layer of frosting over the cake, then chill 15 minutes before adding the final coat. This crumb coat catches loose crumbs and gives you cleaner edges and smoother sides.
Adjust peppermint strength gently: Peppermint extract is strong, so start with the listed amount and add drops only if you want more. Too much turns the flavor sharp and toothpaste-like instead of fresh and cool.

Nutrition Facts ^*

Energy	574	kcal
Protein	6	g
Total Fat	28	g
Carbohydrates	80	g
Dietary Fiber	3	g

^* Approximate, per serving.
Data source: USDA FoodData Central.

FAQ

Why is my cake batter so thin, and is that okay?: This batter is meant to be quite thin because of the hot coffee and buttermilk. It bakes into a very moist, tender crumb, so do not add extra flour to thicken it.
My cake sank in the middle; what went wrong?: Cakes often sink when the oven door opens early, the cake is underbaked, or the leavening was mismeasured. Bake until the center springs back lightly and the toothpick shows just a few moist crumbs, not wet batter.
Can I bake this as cupcakes instead of a layer cake?: Yes, divide the batter into lined muffin tins, filling each about two thirds full. Bake at 350°F for about 18 to 22 minutes, then cool before frosting with the green buttercream.
How far ahead can I make the cake and frosting?: You can bake the cake layers up to two days ahead, wrap tightly, and keep them at room temperature. Buttercream keeps in the fridge for three to five days; just bring it to room temperature and rewhip before using.
How should I store leftovers, and can I freeze the cake?: Store leftover slices covered at room temperature for one day, or in the fridge for up to four days. For longer storage, wrap unfrosted or frosted layers well and freeze for up to two months.

Serving Suggestions

This St. Patrick's Day cake makes a gorgeous centerpiece, especially topped with gold sprinkles or chocolate coins for a pot-of-gold moment.

Serve slices with cold milk, hot coffee, or an Irish coffee for adults to match the deep, cozy chocolate flavor.

Recipe by Eunice.
“I learned to cook by standing in my grandma’s kitchen, watching her turn simple ingredients into meals that fed our entire family. That’s where it started. Today, I create recipes for real life, real kitchens, and anyone who wants good food without overthinking it.” Read more.

Reviews

irene_meals, Boise: is the green food coloring gel just the regular one in the baking aisle. — 4 ★

Eunice: Yes, regular green gel food coloring from the baking aisle works. Start with a few drops, then adjust.