Birthday sheet cake

Ingredients

Cake

• 3 cups (380 g) cake and pastry flour (see Note)
• 2 tsp baking powder
• 1 tsp baking soda
• 1 tsp kosher salt
• 1½ cups (375 ml) buttermilk
• 2 tsp vanilla extract
• ¼ tsp almond extract
• 2 cups (400 g) granulated sugar
• 85 g unsalted butter, room temperature
• ⅓ cup (85 ml) vegetable or canola oil
• 4 eggs, room temperature

Frosting

• 200 g milk chocolate, roughly chopped (about 1½ cups)
• 70 g unsalted butter
• ½ cup (120 g) sour cream
• 1 tsp vanilla extract
• ½ tsp instant espresso powder, optional
• ½ tsp kosher salt
• 2½–3 cups (325–390 g) icing sugar
• Sprinkles, optional

Cooling time: at least 1 hour.

Instructions

1. Preheat your oven to 175°C (350°F) and grease a 23 cm x 33 cm (9 in x 13 in) baking pan with cooking spray.
2. Sift together the flour, baking powder, baking soda and salt in a medium bowl.
3. Combine the buttermilk, vanilla extract and almond extract in a glass measuring cup or small bowl.
4. Beat together the butter and sugar using a hand mixer or in a stand mixer fitted with a paddle attachment. Add the oil and eggs and beat on high until the mixture is a little lighter in colour and texture. Scape down the bowl and beat in the buttermilk mixture. Add in the sifted dry ingredients in three additions, mixing each addition in just until incorporated before adding the next.

5. Spread the batter into the prepared pan and bake for 30 to 35 minutes or until golden brown and a skewer inserted into the centre comes out clean. Cool to room temperature.
6. Make the icing by melting the chocolate and butter together in a medium heatproof bowl set over a pot of simmering water. When melted, remove the chocolate mixture from the heat and stir in the sour cream, vanilla, espresso powder and salt. Gradually beat in 2½ cups of icing sugar, adding more to reach a spreadable consistency.
7. When the cake is cool, either leave the cake in the pan or turn it out onto a serving plate, and spread the frosting overtop. Scatter sprinkles over the cake, if using, and cut to serve.

Note

• Cake and pastry flour, available from some supermarkets and specialist retailers, usually has a finer texture and lower protein content, which yields a tender cake crumb, but you can easily use plain flour instead in this recipe.