Make the cake: preheat oven to 375

Butter sides of 11-inch cake pan with 2tbsp melted butter.

Cut 2 strips parchment paper 20in long and 4in wide. Arrange strips in an 'x' over bottom of pan, with the ends hanging over the edges. (This will help unmold the cake.)

Combine walnuts, flour, cornmeal, and sugar in food processor and pulse until texture resembles fine breadcrumbs. Turn off machine and add vanilla, lemon zest, egg yolks, and 1/4 melted butter. Pulse 6 times for 3 seconds at a time. It will form a sticky, wet sand-like dough.

Spoon "wet sand" into cake pan as even,y as possible. (It will not look like cake batter but will come together as it cooks). Place in oven and bake for 1 hour. Let cool in pan on wire rack.

Make the sauce:

Combine berries, lemon juice, and sugar in a saucepan, and cook over medium until berries break down to form a sauce. Let cool to room temperature.

To serve: dust cake with icing sugar if desired. Whip cream until soft peaks. Serve with sauce and whipped cream on the side.