Preheat oven to 350F. Lightly butter or oil a 9-inch springform pan. Dust with flour and set aside.
In a mixing bowl, stir together flour, baking powder and salt.
In a large bowl, beat the butter and sugar until fluffy and light. Add eggs, one at a time, and beat until blended. Gradually add the flour mixture and beat until well mixed.
Pour batter into springform pan and spread evenly. In a bowl, lightly mix the raspberries with some flour (about 1 teaspoon), sugar (about 1 tablespoon) and lemon zest. Spoon berry mixture over batter and bake about 1 hour. Test for doneness with a toothpick. Cool on a wire rack, then remove from pan. Sprinkle with confectioner's sugar and serve.