Line the bottom of a 9-inch springform pan with parchment paper. Position an oven rack in the middle of the oven and preheat the oven to 325 degrees F.
Place the butter, sugar, vanilla, and lemon zest in the bowl of an electric mixer or large bowl with an electric hand mixer; beat until light and pale in color. Add the lemon juice; mix well, scraping down the sides of the bowl as needed. Add the egg yolks (reserve whites) one at the time, beating well with each addition, scraping down the sides, as needed. Fold in the almond meal and ricotta.
In a separate bowl, use an electric mixer to beat the egg whites until stiff peaks form, about 5 minutes on high. Gently fold the egg whites into the ricotta mixture.
Pour the batter into the prepared cake pan, level of the surface, sprinkle with almonds, and then place in the oven to bake for 50-60 minutes. Leave to cool in a pan for 20 minutes before removing the sides of the pan. Dust with powdered sugar before slicing and serving.