Preheat the oven to 350 degrees F. Brush a 9-inch springform pan with butter or oil.
Sift the flour, baking powder, baking soda, cardamom and salt together in a bowl and set aside. In a standing electric mixer or with a hand-held beater, cream the butter and sugar together at medium speed until light and fluffy. One at a time, add the whole eggs, then the yolks, beating thoroughly after each addition. Alternate mixing in the dry ingredients with the sour cream, a third at a time. Pour the batter into the prepared cake pan. Bake for 45 minutes or until the cake is lightly browned and pulls away from the sides of the pan. It should be slightly springy to the touch. Cool on a rack for 5 minutes, remove the sides of the springform, and cool completely on the rack.
While the cake is baking, make the filling: By hand or in a standing electric mixer, whip the cream and ricotta cheese to the consistency of stiffly-whipped cream. It is very important to have the filling the right consistency. Sift and fold in the confectioners' sugar and the vanilla. Chill until ready to use. Set aside 1 to 3 nice-looking strawberries for garnishing the top of the cake. Stem and slice the remaining strawberries into thirds or halves, depending on their size. Place them in a bowl, sprinkle with the granulated sugar, and set aside to macerate.
Using a serrated knife, cut the cake horizontally into 2 layers. Lay the layers, cut side up on a clean work surface. Drizzle any collected strawberry juice over both cake layers. Spread a third of the cream filling on the bottom layer, arrange strawberry slices over the cream, then cover with another third of the cream. Cover with the other layer of cake. Spread the remaining cream evenly over the top and place the garnishing strawberries in the center of the cake. Transfer the cake to a platter and chill until ready to serve.
