Heat oven to 190C/170C fan/gas 5. Line a 27 x 18cm baking tin with baking parchment.
Rub the butter into the flour, almonds and sugar to make crumbs, then firmly press two-thirds onto the base and sides of the tin. Toss the gooseberries with the caster sugar, then scatter over the top.
Mix the flaked almonds into the remaining crumbs, then scatter over the gooseberries. Bake for 50 mins-1 hr until golden and the fruit is bubbling a little around the edges. Dredge with caster sugar, then cool in the tin. Cut into about 8 squares and enjoy with a cup of tea or serve as a pudding with custard or cream.