Makes about 3 dozen 2-inch cookies
PREPARE THE COOKIES: In the bowl of an electric stand mixer fitted with the paddle attachment, beat together the crème fraîche, butter, and powdered sugar until light and fluffy. Mix in the vanilla and egg until combined.
In a medium bowl, sift together the flour, baking powder, and salt. Add the flour mixture and lemon zest to the butter mixture and beat until evenly incorporated.
On a floured work surface, shape the dough into two 5-inch round disks, wrap tightly in plastic wrap or parchment, and refrigerate for at least 1 hour or up to 3 days. (Alternatively, you can freeze the disks, wrapped tightly in plastic wrap and foil, for up to 1 month. Thaw in the fridge for a day before using.)
Preheat the oven to 350°F. Line 2 baking sheets with parchment paper. Remove the dough from the refrigerator and let it rest on the counter for 5 minutes.
Dust a work surface and rolling pin with flour. Give the disks a few whacks with the rolling pin to soften them slightly. Roll out the dough to a 1/4-inch thickness. Working quickly so the dough won’t soften too much, use cookie cutters to punch out whatever shapes you like. Transfer the cookies to the prepared sheets, rerolling the dough scraps as you go to cut out more cookies.
Bake the cookies for 9 minutes, until the cookies are set but still pale and underdone. Transfer to a wire rack to cool slightly. Leave the oven on and set the lined baking sheets aside.
CREATE THE CANDIED FLOWERS: Set up a work station. Gather your edible flowers together. Place the egg white in a small bowl and the turbinado sugar in a second small bowl. Set out a small paintbrush. Gently dunk a flower in the egg white, taking care to get egg white in between the petals for an even pressing, then press the flower into the cookie. The delicate petals may curl up, but smooth them down with your finger. When the flower is as flat as possible, use the paintbrush to brush a thin coating of additional egg white over the entire surface of the cookie. Sprinkle with a generous pinch of the turbinado sugar. Transfer the flower-topped cookies back to the baking sheets as you work.
Return the cookies to the oven and bake for 7 to 8 minutes, until the edges of the cookies are golden. Transfer to a wire rack to cool.
Note: Make sure to purchase edible, untreated, organic flowers for this, or grow your own. Keep in mind, the colors of the flowers you select will darken as you bake them, giving an antique color effect.