Nutty Rhubarb Cake

This was going to be a rhubarb and almond cake, but I couldn't find the flaked almonds I was sure I had, so it became a cake with mixed nuts - ground almonds in the cake batter and chopped toasted hazelnuts on top. It's a recipe I've used many times before - a shortbread/scone-like dough sandwiching a layer of cooked rhubarb  - and it's become a family favourite. The dough is lighter than pastry but not as soft as a cake.

Ingredients
150g butter
150g caster sugar
1 large egg
a few drops almond extract (optional)
250g SR flour
50g ground almonds
about 400g of rhubarb (cooked with 50g sugar and drained of juice)
25g chopped toasted hazelnuts

Method
Preheat the oven to 180C and grease and base-line a 20cm (8") springform tin.
Melt the butter in a large bowl, in the microwave (or in a saucepan on the hob).
Add the sugar and stir until evenly mixed, then beat in the egg and the almond extract, if using.
Stir in the flour and ground almonds to give a soft dough.
Spread 2/3 of the dough into the bottom of the prepared tin, working the dough up the edge of the tin to make a shallow wall.
Put the fruit onto the base, making an even layer level with the top of the wall of dough.
Using fingers, break the remaining dough into small pieces and scatter over the fruit, spreading the dough to cover as much of the filling as possible, There will be gaps in the dough but these fill up as the dough spreads and rises during baking.
Sprinkle over the chopped hazelnuts and press lightly into the dough.
Bake for around 50-60 minutes, until the dough is golden brown and feels firm; cool in the tin.