4 tablespoons (1/2 stick) unsalted butter, melted and cooled to room temperature
Nonstick cooking spray
2 cups (8 ounces) fresh raspberries
Whipped cream, for serving (optional)
Preheat oven to 425 degrees with a rack positioned in the top third of the oven.
Sift together flour and baking powder in a large bowl. In another large bowl beat eggs until creamy and yellow. Whisk in buttermilk, vanilla, 5 tablespoons plus 1 teaspoon sugar, and butter (mixture will look curdled and broken). Slowly add flour and whisk until batter is smooth and combined.
Spray 8 standard-size (3-ounce) nonstick muffin pan cups with nonstick cooking spray. Divide batter evenly among prepared muffin pan cups, filling about two-thirds full. Transfer to oven and bake until sides of cakes are evenly browned (check by inserting a knife tip between the rim of cake and muffin cup, pulling gently to expose side of cake), about 9 minutes. If cakes are not evenly browned, they will not hold together when inverted. Continue baking, checking every minute, until evenly browned.
Meanwhile, place raspberries in a medium bowl; add remaining 4 tablespoons sugar and gently toss to coat.
Invert cakes onto eight individual plates. Place berries on top and alongside cakes; serve with whipped cream, if desired.