Pear Upside-Down Cake

Preheat oven to 350° F. Butter pan; line bottom with a parchment-paper round. Whisk flour, cornmeal, baking powder, and salt in a small bowl. Stir 1/4 cup sugar and 2 tablespoons water in a small saucepan over medium-low heat until sugar dissolves. Increase heat to medium-high. Boil syrup without stirring, occasionally swirling pan and brushing down sides with a wet pastry brush, until sugar turns dark amber, 8-10 minutes. Remove pan from heat; add 1 tablespoon butter (caramel will bubble vigorously) and whisk until smooth. Pour caramel into prepared cake pan and swirl to coat bottom.
Peel, halve, and core the pears. Place flat on a work surface and cut lengthwise into 1/8"-thick slices. Layer slices over caramel, flat side down, overlapping as needed.
Mix remaining 3/4 cup sugar, 8 tablespoons butter, and vanilla in a large bowl. Using an electric mixer, beat on medium speed until light and fluffy, about 3 minutes. Add yolks one at a time, beating to blend between additions and occasionally scraping bowl. Beat in flour mixture in 3 additions, alternating with milk in 2 additions, beginning and ending with flour mixture.
Using clean, dry beaters, beat egg whites on low speed in a medium bowl until frothy. Increase the speed to medium and continue to beat until whites form soft peaks. Fold about 1/4 of the whites into cake batter. Add in remaining whites; gently fold just to blend. Pour batter over pears in pan; smooth top.
Bake cake, rotating pan halfway through, until top is golden brown and a tester inserted into the center comes out with a few small moist crumbs attached, about 1 hour. Let cool in pan on a wire rack for 30 minutes. Run a thin knife around inside of pan to release cake. DO AHEAD: Can be made 1 day ahead. Store airtight at room temperature.
Invert cake onto a plate; remove parchment paper. Serve warm or at room temperature with whipped cream or caramel gelato, if desired.