Heat the oven to 180C/160C fan/gas 4, butter a 20cm square tin and line with baking parchment. Beat 200g of the butter and 200g of the sugar together in a large bowl using an electric whisk until light and fluffy. Beat in the eggs, one at a time, until well combined. When smooth and creamy, add 225g of the flour, the baking powder, almonds, milk and vanilla, and mix to combine.

Scrape the mixture into the tin and level the surface with a spatula. Dot over teaspoons of jam, then scatter over the blackberries, pressing them in gently.

To make the crumble topping, weigh the remaining 25g butter and 25g sugar into a bowl, add the rest of the flour and a pinch of salt. Rub the ingredients together between your fingertips until they are a crumbly consistency. Mix in the flaked almonds, then scatter the crumble over the cake. Scatter with the 1 tbsp caster sugar and bake for 45 mins until a skewer inserted into the middle comes out clean.

If the cake isn’t ready, return to the oven for 5-10 mins more, then check again. Leave to cool for at least 20 mins in the tin before slicing and serving.