Plum and Polenta Cake

INGREDIENTS

• 13 tablespoons butter, softened
• 1 cup all-purpose flour
• 1/2 cup plus 2 tablespoons finely ground cornmeal or semolina flour
• 1 teaspoon grated lemon zest
• Pinch of kosher salt
• 3/4 cup granulated sugar
• 1 1/2 teaspoons baking powder
• 2 large eggs
• 4 large egg yolks
• 2 tablespoons packed light brown sugar
• 1 teaspoon pure vanilla extract
• 4 plums, cut in half and pitted