Polenta and Pear Upside-Down Cake

Heat oven to 325 degrees F. Peel, halve, core, and slice the pears into 1/4-inch thick wedges. In a large bowl, toss the pears with the lemon juice and set aside. Melt 6 tablespoons butter and pour it into a 10-inch round cake pan, rotating pan to spread evenly. Sprinkle the brown sugars over the melted butter. Slightly overlap the pear slices decoratively in the cake pan. Combine the flour, polenta, baking powder, and salt in a bowl and set aside. Lightly beat the eggs, milk, and vanilla together in a small bowl and set aside. Beat the remaining 8 tablespoons of butter and granulated sugar in a large bowl using an electric mixer set on medium-high speed until pale and smooth. Reduce speed to low and alternately mix in the flour mixture and egg mixture, ending with the flour mixture. Pour the batter into the pan and bake until golden brown and a tester inserted in the center comes out clean, about 1 hour and 10 minutes. Cool in the pan and on a wire rack for 10 minutes, then run a small, sharp knife around the edge of the pan to release the cake and cool completely before serving.