Preheat oven to 350F. Prepare pan by spraying lightly with nonstick cooking spray, then line bottom with parchment round and spray again.
Rub lemon zest into sugar, using your fingers. In medium bowl, whisk together flour, lemon sugar, baking powder and salt.
In a large bowl, whisk together eggs, 1 ½ C ricotta, vanilla extract, almond extract, and lemon extract.
Gently fold dries into wets until thoroughly combined.
Fold in melted butter until combined, then scrape batter into prepared pan.
Whisk egg white until frothy and white, saving the yolk for another purpose. Add sliced almonds and sugar, folding to incorporate.
Dollop the almond topping on top of the cake batter, spreading it out into an even layer and lightly pressing it into the batter with the back of a spoon.
Bake cake until golden brown and a tester inserted into the center comes out clean, 45–55 minutes. Let cool at least 20 minutes before unmolding.
While cake bakes, make the whipped ricotta (if using). Strain ricotta in a mesh strainer lined with a damp paper towel or cheesecloth for about 20 minutes. In the meantime, blitz the sugar until superfine (but not powdered). Add strained ricotta, lemon zest, juice, vanilla extract, and sugar to a food processor fitted with the blade. Whip for about 5 minutes total, scraping the sides every few minutes. (I know 5 minutes sounds long, but thats how to get it nice and fluffy!) Serve cake warm or room temp with dollop of sweetened ricotta. Enjoy!