Drain the ricotta for a few minutes until thick but not wet, then line a springform pan with parchment and lightly grease the sides.
Beat the softened butter and granulated sugar until pale, smooth, and creamy.
Add egg yolks one at a time, then mix in ricotta, lemon zest, vanilla extract, and almond extract until silky.
Stir in almond flour and salt just until combined, stopping as soon as no dry spots remain.
Whip egg whites to firm peaks, then gently fold them into the batter using light strokes.
Pour batter into the prepared pan, smooth the top, sprinkle with slivered almonds, and bake at 350°F (175°C) for 55–60 minutes until lightly golden with a slight center wobble.
Cool completely, then dust with powdered sugar before serving.