Preheat the oven to 350°F. Lightly grease a half-sheet pan (13" x 18"), line it with parchment, and lightly grease the parchment., To make the cake: In a small bowl, mix together the almond flour, baking powder, and salt until evenly blended. Set aside., In a large bowl, beat the egg yolks and brown sugar until the mixture is very light and falls in thick ribbons from the beater, about 3 minutes. Stir in the almond extract then fold in the dry ingredients., In another bowl with clean beaters, whip the egg whites until stiff peaks form. Fold a quarter of the whites into the yolk mixture to lighten it, then fold in the rest just until combined., Pour the batter into the prepared pan, spreading it to the edges and into the corners with an offset spatula, quickly with as little back and forth as possible., Bake the cake for 15 to 18 minutes, until the top is golden brown and a cake tester inserted in the center comes out clean., Remove from the oven and cool completely in the pan. Note: unlike a typical jelly roll, you don't roll this in a towel while still warm; it's too fragile. , For the frosting: Whip the cream until soft peaks form. Sift the cocoa powder over the cream, then whip just until stiff peaks form. Fold in the sugar and liqueur., To assemble: Run a thin spatula around the edges of the cake to loosen it. Dust the top of the cake with confectioners’ sugar. Place a kitchen towel or piece of parchment over the cake. Place another sheet pan on top, and flip the entire cake over. Remove the pan and parchment from the bottom of the cake., Spread two-thirds of the frosting over the cake, leaving one inch of one long side bare. Starting with the uncovered long side, roll the cake into a log and place on a serving platter, seam side down. Cover the outside of the cake with the remaining frosting, and refrigerate until ready to serve., The cake is better when served the next day, as it becomes moister and more tender. Store leftovers in the refrigerator for up to 3 days.