Preheat oven to 375 degrees F. For biscuits, combine dry ingredients in a bowl. Cut in butter until mixture is a crumble (butter forms into pea-sized bits). Mix in zest. Gently stir in buttermilk and sour cream and mix until just incorporated.
Turn dough onto a lightly floured surface and gently knead just until it holds together. Pat out into a circle that's 1-inch thick. With a 3-inch round cookie cutter, or an open-end of a glass, cut dough into 6 rounds and place on a baking sheet. Brush tops lightly with beaten egg. Bake in the middle of the oven 18-20 minutes, until puffed and golden. When cool, cut biscuits in half and set bottom half on dessert plates. Top with cream and fruit, then top with other half of biscuit. If desired before serving, dust with icing sugar and garnish with mint.