lemon zest and orange zest, and toss to coat the zest with flour. spoon the mixture into the bowl of batter and stir with a wooden spoon until thoroughly blended. scrape down the sides of the bowl and mix once more. set aside for 10 minutes to allow the flour to absorb the liquids.
5. stir about 3/4 of the grapes into the batter. spoon the batter into the prepared cake pan and smooth out the top with a spatula.
6. place the pan in the center of the oven. bake for 15 minutes, then sprinkle the top of the cake with remaining grapes. bake until the top is a deep golden 