275g beetroots, leaves removed
250g butter, softened, plus extra for greasing
250g dark chocolate, in drops or broken into pieces
300g caster sugar
75g plain flour
50g cocoa powder
½ tsp baking powder
Prepare the beetroots – trim the stalks to about 2cm from the end, then wash carefully under a cold tap. Do not scrub, simply rub off any dirt with your fingers. You don’t want to damage the skin otherwise the beetroots will ‘bleed’ while cooking.
Put the beetroots in a saucepan and cover with cold water. Bring to a simmer, then cover with a lid and continue to simmer for between 30 mins-1 hr, depending on the size and age of the beetroots. They are cooked when their skins rub off easily and they’re tender when tested with a knife.
Rub off the skins and discard, then cut the beetroots into chunks. Put in a food processor and whizz for a few mins to form a smooth purée, then set aside.
Heat oven to 180C/160C fan/gas 4. Prepare a 20cm square cake tin. If using one with a removable base, grease the sides and line the base with baking parchment, otherwise line both the base and sides of the tin.
Put the chocolate in a heatproof bowl and set over a pan of simmering water. Leave until just melted, stirring occasionally, then remove from the heat and set aside. Cream the butter in large bowl until soft or in an electric food mixer. Add the sugar and beat until the mixture is light and fluffy. Whisk the eggs together in a small bowl, then gradually add to the creamed mixture, beating constantly.
Beat in the beetroot purée and chocolate, then sift in the remaining ingredients with a pinch of salt, folding in until fully combined. Tip the batter into the prepared tin, smoothing the top with a palette knife or spatula. Bake for 30-35 mins or until the centre of the cake is almost set but wobbles slightly when you gently shake the tin. Remove from the oven and cool on a wire rack.
Leave in the tin for at least 1 hr before carefully removing the cake and cutting into squares to serve. If you can resist them, these will keep in an airtight container for a few days.