Hazelnut tray bake

I love traybakes, so I've treated myself to a new tin - the Wilton 'Biscuit/Brownie' pan [28x18cm]. Now I'm fired up to try it out!
I bought some hazelnuts in Waitrose recently, so thought I'd make something using them.
This recipe is adapted from one that was in a magazine some time ago. I like the idea of a crumble base and then the cake mixture on top of it.

300g plain flour
175g butter cut into pieces
350g demerara sugar
200ml creme fraiche
2 eggs

3 tspns baking powder [level]

150g hazelnuts chopped in half

preheat oven 180C/gas4
Grease and line the tin with baking parchment.
Sift flour into a bowl and rub in the butter. Stir in the sugar. Sprinkle 350g of this mixture into the tin and press it down.
Beat the eggs and creme fraiche together and stir in the rest of the crumble mixture and baking powder.
Pour this over the crumble mixture. Arrange the hazelnuts on top, pressing gently.
Bake in middle of the oven for about 45 mins. I found that the nuts were getting too brown, so I covered them with parchment.

Now comes the fiddly bit! You need to get the bottom crumble crisp, so put a piece of parchment over the cake and put a baking sheet on top. Invert the cake onto the sheet. Take off the lining paper and put the cake back in the oven for about 10-15 mins.

To put it on a wire rack you need to invert the rack over it to get the cake the right way up. It's worth the effort, honestly!

This is what the finished cake looks like. When Bob had a look at the camera, he deleted the good photos!