make the cake
In a large bowl, whisk together the ground almonds, flour, polenta, baking powder, rosemary, lemon zest and salt. In the bowl of a standing electric mixer fitted with the whisk, combine the eggs and sugar and beat at medium-high speed until tripled in volume, 10 minutes. With the mixer at low speed, add the crème fraîche, then drizzle in the melted butter just until incorporated. Using a rubber spatula, gently fold the egg mixture into the dry ingredients in 3 batches. Scrape the batter into the prepared pan and bake for about 30 minutes, until a paring knife inserted in the center of the cake comes out clean.