Preheat oven to 180C (160C fan forced). Line the bottom of the tin with grease proof paper and brush sides with butter.
Mix flour with baking powder and sift. Set aside.
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).
Bake at 180C (160C fan forced) for 50 minutes. When baked, open oven door and let the cake cool in the oven for 10 minutes then take out and give the tin a little bang. The cake is going to deflate around 1 - 2cm when cooling. Run thin knife around the edges to loosen, let it cool for 15-20 minutes, sprinkle with icing sugar and serve. It tastes great when still warm or chilled in the fridge for few hours.