Step 1

Place a rack in middle of oven; preheat to 325°. Lightly coat an 8½x4½" loaf pan with nonstick spray, then line with parchment paper, leaving overhang on long sides.

Step 2

Whisk flour, cornmeal, baking powder, and salt into a small bowl. Using an electric mixer, beat butter and sugar in a large bowl on medium speed until light and fluffy, about 5 minutes. Add eggs and egg yolk one at a time, mixing to fully incorporate before adding the next. Scrape down sides of bowl, add half of dry ingredients, and beat on low speed just to combine. Add sour cream and remaining dry ingredients and mix 1 minute. Scrape down sides of bowl, add ricotta and vanilla, and mix until well combined. Scrape batter into prepared pan; smooth surface.

Step 3

Bake cake 40 minutes. Rotate pan and continue to bake cake until golden brown all over and a tester inserted into the center comes out clean, 20–30 minutes more. (Baking the cake slowly at a lower temperature yields a tender and creamy crumb and will prevent it from drying out.) Let cake cool in pan on a wire rack, at least 1 hour.

Step 4

Carefully run an offset spatula or paring knife around sides of cake and use parchment paper to lift cake from pan; remove parchment. Cut cake into slices and serve topped with whipped cream and/or lemon curd if desired.Do ahead: Cake can be baked 2 days ahead. Store tightly wrapped at room temperature, or freeze up to 2 weeks.