Preheat the oven to 360°F and cover an around 8×8.5-inch round baking pan with parchment paper (or butter well).
Beat the butter with sugar, vanilla extract and lemon zest until obtaining a cream.
Separate the whites from the yolks and beat the egg whites to stiff peaks. Set aside.
Add the yolks to the butter mixture and beat. Then add ricotta, keep beating, and lastly sliced almonds and beat again.
Add the whites with stiff peaks to the mixture, in 3 or 4 parts, adding a couple spoonfuls of egg white and raspberries and mixing with a spatula in folding motion, until there are no peaks left.
Put in a mold, level the surface, and cover it all with sliced almonds.
Bake at 360°F for 60-70 minutes (after an hour, check by inserting a toothpick).
Take out of the oven, leave in the mold for 10 minutes, then unmold. Allow to cool completely over a baking rack and refrigerate.
Decorate with raspberries before serving.