Prepare batter: Mix sugar with lemon zest and cardamom. Using palms of your hands rub zest into sugar to release flavour. Beat soft butter for 1 minute until fluffy. Add 90g of zesty sugar to butter (in 3 lots) and beat until fluffy - about 2-3 minutes. Start adding egg yolks - one at a time, mixing well after each addition. Then start adding Ricotta - 2 Tablespoons at a time - mix well after each addition (paddle attachment, low-medium speed, or handheld mixer - low speed). Add flour - in 2 turns and mix gently (lowest speed) only until combined and no flour pockets remain. Set the mixture aside. In a separate bowl beat egg whites until fluffy (1 minute) then add remaining part of sugar (90g) and beat until firm (2-3 minutes), at the end add coarse salt and beat for few seconds. Fold beaten egg whites into the Ricotta mixture. Pour the batter into the tin, gently place fruit on top (make sure there are some spaces in-between so that the cake has a chance to puff up).