Put oven rack in middle position and preheat oven to 350°F. Generously butter molds and put on a baking sheet.
Whisk together flour, baking powder, zest, and salt.
Beat together butter and sugar with an electric mixer at high speed until pale and fluffy, about 2 minutes. Beat in egg and vanilla until just incorporated.
Add milk and beat until just combined (mixture will appear curdled). Reduce speed to low, then add flour mixture in 3 batches, beating until just combined after each addition.
Divide batter among molds, filling each mold about two-thirds full.
Bake until edges of cakes are golden and a wooden pick inserted in center of a cake comes out clean, about 25 minutes. Cool cakes in molds on a rack 5 minutes, then turn out onto rack and cool completely.
While cakes cool, pulse 1/2 cup each of raspberries, blueberries, blackberries, and strawberries (all together) with 2 tablespoons superfine sugar in a food processor until fruit is just crushed. Chill, covered, up to 2 hours.
Beat cream with remaining tablespoon superfine sugar using cleaned beaters at medium-high speed until it just forms soft peaks. Chill, covered, until ready to serve (but no longer than 2 hours).
Arrange cakes upside down on 6 plates and top each with 2 rounded tablespoons whipped cream and 1 rounded tablespoon crushed berries. Scatter remaining whole berries over top and serve remaining crushed berries on the side.
Cakes can be made 2 days ahead and kept in an airtight container at room temperature, or 2 weeks ahead and frozen, wrapped in plastic wrap and then foil. Thaw frozen cakes in refrigerator and bring to room temperature before serving.
