Heat the oven to 350°F with a rack in the middle position. Generously mist the outer 8 cups of a standard 12-cup muffin pan with cooking spray.

In a medium bowl, whisk together the flour, poppy seeds, baking powder, baking soda and salt. In a blender, combine the buttermilk, butter, whole egg and egg yolk, vanilla and sugar. Blend on high just until combined, about 15 seconds, scraping the jar halfway through to make sure the sugar has not clumped on the sides; do not overblend. Pour the wet ingredients into the dry ingredients, then whisk just until evenly moistened. Scoop the batter into the prepared cups of the muffin pan, dividing it evenly. Rap the pan 2 or 3 times on the counter to remove any air bubbles.

Bake until the cakes are light golden brown and a toothpick inserted at the centers comes out clean, 12 to 15 minutes. Cool in the pans on a wire rack for 5 minutes. Run a paring knife around the edge of each cake to loosen. Lift them out of the pan and set directly on the rack. Cool completely.

When you are ready to finish the cakes, in a medium bowl and using a hand mixer or whisk, whip the cream until soft peaks form. In another medium bowl, stir the lemon curd until loosened. Add about 3 tablespoons of the whipped cream to the curd and, using a silicone spatula, gently fold until just the mixture is lightened and lightly streaked. Add the remaining whipped cream to the lightened curd and fold until the mixture looks swirled.

Using a serrated knife, slice the cap off each cake where it meets the sides; set the caps aside. Spread 1 teaspoon raspberry preserves on the cut side of each cake base. Dollop 1 tablespoon whipped cream onto the preserves on each cake. Place the caps gently on top; do not press them down.

Dollop the remaining whipped cream onto the center of each cake (about 1 tablespoon each), creating a cloud-like puff. Using the back of a small spoon, make a shallow indentation in the center of the whipped cream. Spoon ½ teaspoon of the remaining preserves into each indentation. Garnish each cakes with mint (if using). Serve immediately or refrigerate, uncovered, for up to 1 hour.