This cake is moist, full of flavour, and the perfect cake for spring!
Preheat oven to 350F and grease a 10" round baking dish or pan.
In a clean medium sized bowl, beat the egg whites on high with a hand mixer or stand mixer until soft peaks start to form. Slowly add ¼ cup of the sugar while beating until stiff peaks form. Set aside.
In a large bowl, beat the butter with the mixer until light and fluffy, about 3 minutes.
Add the remaining ¾ cup sugar, vanilla, egg yolks, ricotta cheese, lemon zest and lemon juice, and beat on medium until smooth. Add the ground almonds, flour, baking powder and salt and beat again on medium speed until just combined.
Fold in 1/3 of the egg whites until incorporated, and then gently fold in the remaining egg whites just until the batter is smooth. Doing this step gradually makes it easier to mix in the egg whites without deflating them.
Spread the batter into the prepared pan and even it out with the back of a spatula. Sprinkle the cake evenly with the sliced almonds and bake for approximately 40 minutes, until the cake is lightly browned on the edges and the edges start to pull away from the sides of the pan. A toothpick inserted in the centre will come out clean.
Cool the cake and sprinkle with icing sugar if you wish and serve.