Adjust oven rack to lower-middle position and heat oven to 450 degrees. For easy cake removal, generously grease and flour 24 mini-muffin tins, or line with cupcake liners.
Mix flour, cornstarch, baking powder, and salt in a large bowl. Mix milk, egg, and vanilla in a small bowl. Beat softened butter into dry ingredients, first on low, then increase to medium, until mixture forms pebble-size pieces. Add milk mixture slowly, beating until smooth. Add sugar; beat until just incorporated, about 30 seconds. Pour batter into prepared muffin tins and bake until a cake tester or toothpick inserted into cake’s center comes out clean, 8 to 10 minutes.
Remove muffin tins from oven; let cool for a few minutes. Transfer pans to freezer; let cool until solid to the touch. Run a knife around each muffin’s perimeter and remove from pan.
Meanwhile, melt chocolate in a double broiler or microwave.
Working one at a time, spread each cake with a heaping teaspoon of peanut butter and then dip into melted chocolate. Place on a cooling rack until set. Serve at room temperate or straight from the fridge.
Recipe by Three Many Cooks at https://threemanycooks.com/conversations/honeymoon-plus-five/