Line a 9″ spring form well with the softened butter. Swirl the breadcrumbs all around and on the bottom of the pan so they stick to the pan. Dump out any extra breadcrumbs.
Place the ricotta in a cheesecloth lined sieve and place the sieve over a bowl and let drain for 3-4 hours in the refrigerator. In a mixer, whisk the eggs, sugar, and salt until frothy and pale yellow. Add the drained ricotta, sour cream, and lemon zest, and whisk until blended thoroughly. Add 1/3 cup of the reserved amarene syrup and slowly add the flour. Whisk until the mixture is smooth. Pour the cake mixture into the prepared pan, and scatter the amarene cherries on the top of the cake batter. With the tip of a skewer, slowly mix the cherries, and let them partly sink into the batter. Set on a sheet pan and set in a 350-degree preheated oven. Bake until the cake is golden brown on top and set in the center, about 1 hour 30 minutes. Cool the cake completely before removing from the spring form.
Serve the cake at room temperature, or chilled, topped with some more amarene cherries and their syrup.
