Preheat the oven to 200C/180C Fan/Gas 6. Line an 8 inch square baking tin.
Combine the melted butter, granulated sugar and light brown sugar in a large mixing bowl or the bowl of a stand mixer. Combine on high speed for 3-5 minutes.
Add the eggs, vanilla, lemon zest and juice and combine again.
Fold in the flour, baking powder, white chocolate chunks and raspberries, using a wooden spoon/silicone spatula. If using fresh raspberries, stir these in last to prevent breaking up!
Pour the batter into the prepared tin. Dollop on the jam and swirl through the blondie batter. Bake for 30 minutes, until golden on top. Let cool on a wire rack.
