How to Make It
Preheat the oven to 350°. Butter an 10-inch springform pan.
Spread the almonds on a rimmed baking sheet and bake for about 4 minutes, until they are slightly fragrant. Let the almonds cool completely, then coarsely chop them. In a food processor, pulse the almonds until they are finely ground but not pasty.
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.
In a small saucepan, combine the water, sugar and lemon juice and boil for 3 minutes. Let cool.
Set the hot cake on a rimmed baking sheet and pour the syrup evenly over it. Let the cake cool completely. Remove the side and bottom of the pan and transfer the almond cake to a platter.
In a medium bowl, whisk together the confectioners’ sugar, crème fraîche and lemon juice until smooth. Spread the glaze all over the top of the cake. Let stand until the glaze sets slightly, then cut into wedges and serve.