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["Preheat oven to 350u00b0F. Butter a 9""-diameter cake pan and line bottom with a round of parchment paper; butter parchment.", "Melt 3/4 cup butter in a medium saucepan over medium heat, then cook, stirring often, until butter foams, then browns (do not let burn), 5-8 minutes. Pour into a medium bowl; let cool. Chill brown butter until cold.", "Fit a clean medium saucepan with thermometer and bring maple syrup to a boil over medium-high heat; cook until thermometer registers 265u00b0F (syrup will be thicker and a shade darker). Pour into prepared pan and spread with an offset spatula or a spoon to cover bottom; let cool (syrup will harden as it sits).", "Whisk almond flour, polenta, baking powder, and salt in a medium bowl. Using an electric mixer on medium-high speed, beat chilled brown butter and 3/4 cup sugar until very pale and fluffy, 5-7 minutes. Add eggs 1 at a time, beating to blend between additions. Beat until light and fluffy, about 4 minutes. Reduce speed to low, gradually add dry ingredients, and mix just to combine. Scrape batter into pan; smooth top.", "Bake until cake is golden brown and pulls away from sides of pan, 50-55 minutes. Transfer pan to a wire rack; let cake cool in pan 20 minutes. Turn out onto rack and let cool completely.", "Using an electric mixer, beat heavy cream, sour cream, and remaining 1 tablespoon sugar in a medium bowl until soft peaks form. Serve cake with whipped-cream mixture.", "DO AHEAD:"]
