cherry cornmeal upside-down cake

INGREDIENTS

• 10. As if I couldn’t have possibly done one more thing that evidenced my compromised logic that evening, I succumbed to a slice of it at 12:00 a.m. And do you know what happened? I was so hopped up on sugar, I couldn’t get to sleep until after 1 a.m. But
• 3/4 cup (1 1/2 sticks) unsalted butter, room temperature, divided
• 1/4 cup (packed) dark brown sugar
• 2 teaspoons balsamic vinegar
• 3 cups whole pitted fresh Bing cherries or other dark sweet cherries (about 21 ounces whole unpitted cherries)
• 1 1/4 cups all purpose flour
• 1/4 cup yellow cornmeal (preferably stone-ground medium grind)
• 2 teaspoons baking powder
• 1/4 teaspoon salt
• 1 cup sugar
• 2 large eggs, separated
• 3/4 teaspoon vanilla extract
• 1/2 cup whole milk
• 1/4 teaspoon cream of tartar