Special equipment: an offset spatula, a silicon pad, a baking sheet, a small muffin tin
Put the strawberries on a flat surface and cut them, widthwise, into 1/4-inch thick slices. The slices should be thin enough to bend slightly when you cut them.
Using a vegetable peeler and, with a light touch, remove the zest from half of the lemon. Try to remove the zest in small pieces and leave the pith (the white part) behind. Juice the lemon and the lime and add them to a bowl along with the zest, sugar and strawberries. Cover the bowl and refrigerate.
Preheat the oven to 375 degrees F. Meanwhile, sift the powdered sugar and flour into a medium bowl. Use your hands to push the sugar and flour through the strainer to make it easier. Stir in the melted butter and the orange juice. Stir to blend.
Invert a baking sheet and put it on a flat surface. Coat it with a thin layer of nonstick spray as an added precaution against sticking. Spoon a generous teaspoon of the batter near the corner of the sheet and use a small offset spatula to spread it thinly into a small, imperfect oval. Take care to leave space between each oval because they will spread when they are baked. You should be able to fit about 12 on the tray.
Bake them in the oven until light brown, about 5 to 8 minutes. Remove the tray from the oven. Put the tray by the inverted muffin tin. Use the offset spatula to lift the shells, 1 by 1, off the tray. Using your fingers, put a shell over the muffin tin bottom, pressing down to create a tart shell. The sides will overlap or be higher than the muffin hole. Your goal is to make a tart shell to fill with the strawberries. Repeat with the remaining shells. Allow them to cool.
Strain the liquid from the strawberries and pour it into a small pan. Reduce over medium heat until it becomes syrupy and thick. Pour it back over the strawberries and toss to blend. Return to the refrigerator to chill again. When ready to serve, put a small dollop of sour cream in the bottom of each shell and top with some of the strawberries. Sprinkle with a touch of granulated sugar. Serve immediately.
If the ovals cool too much on the baking sheet and aren't flexible, put the tray back in the warm oven for a minute to loosen them up and resume molding them into the muffin tin.
Recipe courtesy of Alex Guarnaschelli