One-bowl chocolate cake with one-minute frosting

In one bowl stir together the flour, granulated sugar, caster sugar, cocoa, baking soda and salt; sift them for insurance against cocoa lumps.

Add the egg, buttermilk, hot water (with espresso powder if using) and vegetable oil.

Whisk just until no flour is visible, without over-mixing; the batter is thin.

Pour into a buttered 8 by 8 pan lined with parchment that stands above the sides to hold the frosting.

Bake at 350F (said as '183 Celsius') for roughly 25 to 30 minutes, until firm under a fingertip.

Microwave the butter, cocoa powder and milk in a bowl for about 45 seconds to a minute, until the butter melts and the mixture boils.

Whisk in the vanilla extract and sifted powdered sugar until smooth and thick.

Pour the frosting over the cake while still warm, so it sets with a crinkle top and soaks into the cake.

Decorate with gold sprinkles before the icing sets.

Let the frosting set about two hours at room temperature, or a few hours in the fridge, before serving.