Coffee and Walnut Cake

Before you start

Coffee and walnut cake is a fixture of British tea rooms and village bakes. It is a classic Victoria-style sponge, made with equal weights of butter, sugar, eggs and self-raising flour, flavored with strong instant coffee and studded with chopped walnuts. The two layers are sandwiched and topped with a coffee buttercream and a ring of walnut halves.

The coffee must be concentrated. Brewed coffee adds too much water for a sponge this rich, so dissolve instant espresso powder in a small amount of hot water instead. Toast the walnuts lightly before chopping; it removes their raw, slightly bitter edge and makes the coffee taste rounder.

Ingredients

• Sponge75 g (¾ cup) walnut pieces — plus 10 halves for the top
• 2 tbsp instant espresso powder
• 2 tbsp boiling water
• 225 g (1 cup) unsalted butter — very soft
• 225 g (1 cup plus 2 tbsp) caster or superfine sugar
• 4 large (about 225 g) eggs — room temperature
• 225 g (1¾ cups plus 1 tbsp) self-raising flour
• 1 tsp baking powder
• Coffee buttercream150 g (⅔ cup) unsalted butter — softened
• 300 g (2½ cups) powdered (icing) sugar — sifted
• 1 tbsp instant espresso powder
• 1 tbsp boiling water
• 1 pinch fine salt

Method

1. Heat the oven to 180°C (350°F), or 160°C on a fan setting. Toast all the walnuts, including the halves, on a tray for 6 to 8 minutes until fragrant. Cool, set the halves aside and chop the rest finely.
2. Grease the tins and line the bases with parchment. Dissolve 2 tbsp espresso powder in 2 tbsp boiling water and let it cool slightly.
3. Put the butter, sugar, eggs, flour and baking powder in the mixer bowl. Beat on medium for about 1 minute, scrape the bowl, then beat for 30 seconds more, until smooth and a little lighter in color.
4. Beat in the coffee, then fold in the chopped walnuts by hand. The batter should drop off a spoon in a soft dollop; if it is stiff, add 1 tbsp milk.
5. Divide the batter between the tins, about 490 g each, and level it. Bake for 22 to 25 minutes, until risen, golden, springy in the center and just shrinking from the sides.
6. Cool in the tins for 10 minutes, then turn out onto a rack, peel off the paper and cool completely.
7. For the buttercream, dissolve 1 tbsp espresso powder in 1 tbsp boiling water and cool. Beat the butter until pale, then beat in the powdered sugar, salt and coffee until fluffy.
8. Place one sponge top-side down on a plate and spread with half the buttercream. Set the second sponge on top, top-side up, spread with the remaining buttercream and arrange the walnut halves around the edge.

Tips for success

• For the all-in-one method the butter must be very soft, almost like mayonnaise, or it will leave lumps that bake into holes.
• Taste the buttercream. Instant coffee strength varies by brand; add more dissolved espresso a teaspoon at a time if you want a bolder finish.
• Spread the top layer of buttercream in a swirl rather than smoothing it flat. It is traditional and hides any doming.

Substitutions

Self-raising flour

Use 225 g all-purpose flour plus 2¾ tsp baking powder and ¼ tsp salt, still adding the extra 1 tsp baking powder from the recipe. Whisk well so the leavening is even.

Instant espresso powder

Use 3 tbsp regular instant coffee granules dissolved in the same amount of hot water. The flavor is milder and a little more bitter.

Walnuts

Pecans give a sweeter, softer flavor and work the same way. For a nut-free cake, leave them out and decorate with chocolate-covered coffee beans.

Variations

Coffee walnut traybake

Bake the batter in a parchment-lined 20 x 30 cm (8 x 12 in) tin for 25 to 30 minutes, spread the buttercream on top and cut into 15 squares.

Mocha version

Replace 25 g of the flour with cocoa powder and beat 30 g melted, cooled dark chocolate into the buttercream.

Troubleshooting

Sponges came out flat and dense

The butter was too cold or the batter was overbeaten until it lost air and turned greasy. Use very soft butter and beat only until smooth.

Weak coffee flavor

Brewed coffee or too little powder was used. Dissolve instant espresso in the smallest amount of hot water you can, and use the buttercream to push the flavor further.

Buttercream looks split or speckled

The coffee was hot when added, or undissolved granules remained. Cool the coffee liquid to room temperature and make sure no grains are left before beating it in.

Storage

Keep the cake in an airtight container at cool room temperature for up to 3 days. In warm weather, refrigerate it and let slices stand for 30 minutes before serving so the buttercream softens. Unfilled sponges freeze for up to 2 months.

Safety notes

Contains tree nuts, wheat, egg and milk. Do not taste the raw batter. The cake contains a modest amount of caffeine from the espresso powder, which may matter for children or caffeine-sensitive guests.