Preheat your oven to 325°F (160°C) and prepare a 9-inch cake pan lined with parchment paper and greased lightly with butter.

In a large electric mixer bowl, combine softened butter, 3/4 cup of sugar, vanilla extract, and lemon zest. Beat on medium-high speed for about 8 to 10 minutes until pale and fluffy.

Gradually add the egg yolks one at a time to the butter mixture, fully incorporating each before adding the next. Gently fold in the almond meal and ricotta until smooth.

In a clean bowl, whisk the egg whites until soft peaks form, about 3-4 minutes. Slowly sprinkle in the remaining sugar and continue whipping until stiff peaks develop.

Carefully fold half of the whipped egg whites into the batter, being gentle to avoid deflation. Repeat with the remaining egg whites.

Pour the batter into the prepared cake pan, smoothing the top. Sprinkle sliced almonds over the surface.

Bake for 40 to 45 minutes until the edges are golden and a toothpick inserted into the center comes out clean.

Cool the cake in the pan for about 10 minutes, then invert onto a serving plate, remove parchment, and cool completely before dusting with powdered sugar.