· Kata

Coffee Walnut Cake with Mascarpone Frosting

A soft Coffee Walnut Cake with rich coffee flavour, crunchy walnuts, and a creamy coffee mascarpone frosting. Simple, classic, and perfect with coffee.

This Coffee Walnut Cake is soft, buttery, and full of rich coffee flavour, with crunchy walnuts throughout the sponge and a creamy coffee mascarpone frosting on top. Coffee is used twice—once in the cake and again in the frosting—giving every slice a deeper flavour without becoming overpowering.

The mascarpone topping is lighter and less sweet than a traditional buttercream, making it a lovely match for the rich coffee sponge. Finished with walnuts, this simple cake is perfect for afternoon tea, weekend baking, or serving with a fresh cup of coffee.

Servings: 8-10 - Prep: 25 min - Cook: 30-38 min - Total: About 1 hour 5 minutes + cooling

Ingredients

For the Cake

  • 2 tbsp instant coffee powder

  • 2 tbsp boiling water

  • 180 g unsalted butter, softened (about ¾ cup + 1 tbsp)

  • 170 g light brown sugar (about ¾ cup + 2 tbsp, packed)

  • 3 large eggs, at room temperature

  • 180 g plain flour (1½ cups all-purpose flour)

  • 1½ tsp baking powder

  • ¼ tsp fine salt

  • 70 g walnuts, chopped (about ⅔ cup)

For the Coffee Mascarpone Frosting

  • 250 g mascarpone, cold (about 9 oz)

  • 60 g icing sugar (about ½ cup powdered sugar)

  • 2 tsp instant coffee

  • 1 tsp boiling water

Optional Decoration

  • A few walnut halves or roughly chopped walnuts

Instructions

1. Prepare the Oven and Tin

Preheat the oven to 180°C conventional / 160°C fan / 350°F. Grease your cake tin and line the base with baking paper.

2. Prepare the Coffee

Place the instant coffee powder in a small bowl and add the boiling water. Stir until completely dissolved, then leave it to cool while you prepare the remaining ingredients. The coffee should be cool before adding it to the cake batter.

3. Cream the Butter and Sugar

Place the softened butter and light brown sugar in a large mixing bowl. Beat for approximately 3 minutes, until lighter, fluffy, and well combined. Scrape down the sides of the bowl as needed.

4. Add the Eggs

Add the eggs one at a time, beating well after each addition. Scrape down the bowl between additions to make sure everything mixes evenly. If the mixture begins to look slightly curdled, add a spoonful of the measured flour and continue mixing.

5. Combine the Dry Ingredients

In a separate bowl, whisk together the plain flour, baking powder, and salt. This helps distribute the raising agent evenly throughout the cake.

6. Finish the Batter

Fold the dry ingredients gently into the butter mixture. Add the cooled coffee and 50 g of the chopped walnuts. Fold everything together only until evenly combined. Avoid overmixing the batter.

7. Fill the Tin

Transfer the batter to the prepared cake tin and spread it into an even layer. Scatter the remaining 15 g chopped walnuts over the surface.

8. Bake

Bake for 30-38 minutes, or until the cake is golden, springs back lightly when touched, and a skewer inserted into the centre comes out clean or with a few fine crumbs. Begin checking the cake after approximately 30 minutes, as ovens can vary.

9. Cool the Cake

Leave the cake in the tin for 15 minutes. Carefully turn it out onto a wire rack, remove the baking paper, and turn it upright again. Allow it to cool completely before adding the mascarpone frosting. Do not frost the cake while it is still warm, as the mascarpone can soften and melt.

Coffee Mascarpone Frosting

10. Prepare the Coffee

Dissolve the instant coffee in 1 teaspoon boiling water. Stir well, then leave it until completely cold. This is important because warm coffee can soften the mascarpone.

11. Mix the Mascarpone

Place the cold mascarpone and sifted icing sugar in a mixing bowl. Mix briefly on low speed, or gently by hand, until smooth. Avoid beating it for too long.

12. Add the Coffee

Add the completely cooled coffee concentrate. Mix gently only until the coffee is evenly incorporated and the frosting looks smooth. Do not overmix. If the frosting becomes softer than you would like, refrigerate it for 15-20 minutes before using.

13. Frost the Cake

Once the cake is completely cold, spoon the mascarpone frosting onto the top. Spread it gently with an offset spatula or the back of a spoon. You can create soft swirls for a simple, rustic finish.

14. Decorate and Serve

Finish with a few walnut halves or chopped walnuts, if desired. Slice and serve with tea or coffee.

Tips and Tricks

✅ Make sure the butter is properly softened before creaming it with the sugar. This helps create a light and tender cake.

✅ Use room-temperature eggs so they mix more easily into the butter mixture.

✅ Add the eggs gradually to reduce the chance of the batter curdling.

✅ If the butter mixture begins to split, add a tablespoon of the measured flour and continue mixing.

✅ Let the coffee cool completely before adding it to the cake batter.

✅ Chop the walnuts roughly rather than too finely so you still get noticeable pieces throughout the sponge.

✅ Fold the flour into the batter gently and stop mixing as soon as everything is combined.

✅ Begin checking the cake at 30 minutes to avoid overbaking and drying out the sponge.

✅ Cool the cake completely before frosting it. Even a slightly warm cake can make mascarpone frosting too soft.

✅ Keep the mascarpone cold until you are ready to make the frosting.

✅ Do not overmix mascarpone. Excessive beating can make it loose, grainy, or watery.

✅ Make sure the coffee used for the frosting is completely cold before adding it.

✅ If the mascarpone frosting becomes too soft, place it in the refrigerator for 15-20 minutes before spreading.

✅ For an even stronger coffee flavour, you can add a little extra instant coffee to the cake, but dissolve it first rather than adding the granules directly.

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