Blueberry Upside-Down Cake

Ingredients

• 1/2 cup unsalted butter
• 1/4 cup light brown sugar
• 3/4 pound blueberries
• 1 1/2 cups flour
• 2 teaspoons baking powder
• 1/4 teaspoon salt
• 1 cup sugar
• 2 yolks
• 1 teaspoon plus a few drops vanilla
• 1/2 cup milk
• 2 egg whites
• 1/4 teaspoon cream of tartar
• 1 cup heavy cream
• 1 tablespoon confectioners sugar