Preheat oven to 350°F Coat a 9 x 12-inch baking sheet with 1-inch high sides with nonstick spray; line with parchment paper and spray again.
Mix together flour, sugar, baking powder, and salt.
In another bowl, blend egg yolks, oil, water, lemon extract, and zest. Gradually whisk flour mixture into yolk-oil mixture until smooth.
Beat egg whites in a bowl with an electric mixer on medium-high speed until frothy. Gradually add 1/8 cup sugar to the whties and continue beating until they-re shiny and hold firm peaks as beaters are lifted out. Whisk 1/3 of the beaten whites into the batter to lighten it; gently fold in the remaining whites with a whisk.
Pour batter onto the prepared baking sheet. Tilt the pan to evenly spread the batter (don't use a spatula--it can deflate the whites), then bake the cake 12-13 minutes, or until just set. Cool to room temperature, remove from pan, peel off paper, and cut into 1 1/2-inch rounds. (Don't cut rounds too big, or assembled cakes will be floppy when picked up).
Whip cream and lemon curd together for the lemon cream, beating to soft peaks. Dollop 1 tablespoon cream on each cake round.
Top cakes with berries, dust with powdered sugar, then garnish with mint. Serve or chill up to 2 hours.