Almond Mascarpone Torte

Preheat the oven and prepare the pan. Preheat to 350°F (175°C). Butter and flour an 8- or 9-inch round cake pan, or line it with parchment. For easier unmolding, place a circle of parchment in the base.
Whisk dry ingredients. In a medium bowl, whisk together the almond flour, all-purpose flour, baking powder and salt. If using lemon zest, fold it into the dry mix so the oils distribute evenly.
Cream butter and sugar. In a large bowl, beat the softened butter and granulated sugar until light and slightly airy (about 2–3 minutes by hand or with a mixer on medium). The mixture should look paler and fluffier.
Add eggs and vanilla. Add the eggs one at a time, mixing well after each addition to ensure incorporation. Stir in the vanilla extract.
Combine wet and dry. Add the dry ingredients to the wet mixture in two additions, folding gently with a spatula until just combined. Avoid overmixing; stop when there are no large streaks of flour.
Transfer and bake. Pour the batter into the prepared pan and smooth the top. Bake on the center rack for 25–30 minutes, or until the top is golden, and a toothpick inserted into the center comes out with a few moist crumbs but not wet batter.
Cool the cake. Allow the cake to cool in the pan on a wire rack for 10–15 minutes. Run a knife around the edge, then invert onto the rack or remove using the parchment. Cool completely before applying the mascarpone layer; if the cake is warm the filling may loosen and become runny.
Make the mascarpone filling. In a chilled bowl, gently whip the mascarpone with powdered sugar and vanilla until smooth. Add heavy cream by tablespoonfuls if you prefer a looser, spreadable texture. Avoid overbeating — mascarpone can separate if whipped aggressively.
Assemble the torte. If desired, split the cake horizontally into two layers with a serrated knife. Spread a generous layer of mascarpone between the layers and then a thin finish layer on top. Alternatively, spread the mascarpone only over the top for a simpler assembly. Chill the completed torte for at least 30 minutes to firm the filling before serving.
Finish and serve. Garnish with toasted almond slivers, a dusting of powdered sugar, or fresh berries. Serve chilled or at cool room temperature.