Heat oven to 180C/160C fan/gas 4. Butter the base of a deep 20cm loose-bottomed cake tin and line with baking parchment.
To make the crumble topping, put the flour and butter in a bowl and rub together with your fingertips until you have a coarse, crumbly texture. Stir through the sugar, then transfer to the fridge.
Beat the butter and sugar with an electric whisk for 5 mins until light and fluffy. Gradually whisk in the eggs, beating well after each addition. Fold in the flour, baking powder, ground almonds and soured cream, then most of the cherries, reserving a handful to garnish. Spoon the mixture into the prepared tin and smooth over the top with a spatula. Dot with the reserved cherries, then bake in the centre of the oven for 30 mins.
Scatter over the crumble topping, then return the cake to the oven and bake for a further 30-50 mins until a skewer inserted in the middle comes out clean. Remove from the oven and leave to cool in the tin.
Slice the cake into thick wedges and serve with custard or ice cream, if you like. Store in a tin or airtight container for up to three days.