Step 1Place the flour and sugar in a large mixing bowl. Add the butter. Using your hands or a pastry cutter, work the butter into the flour until it resembles cornmeal.
Step 2Whisk the egg yolks and cream together in a small bowl. Drizzle the cream and yolk mixture over the flour mixture.
Step 3Mix until the dough comes together. Be careful not to over-mix, which makes the dough tough.
Step 4Remove the dough from the bowl. Divide the dough in half and wrap it in plastic wrap. Flatten into two disks and refrigerate for at least 1 hour. When it is chilled, roll out 1 disk on a lightly floured surface, to a one-fourth-inch-thick round. Using the removable bottom of a 4-inch tart pan as a guide, cut out circles 1 inch larger. Gently fit each circle into the sides and bottom of a tart pan. Remove excess dough by running a rolling pin across the top. Repeat with the remaining dough to line 6 tart pans in total. You will have some extra dough, which may be frozen for another use. Chill the lined tart pans for 30 minutes.
Step 1Heat the oven to 350 degrees with the baking rack at the lowest position. Place the chilled tart shells on a cookie sheet.
Step 2In a medium bowl, lightly whisk together the sugar and eggs. Add the vanilla extract, then the flour, whisking together just until combined. Do not over-beat.
Step 3In a medium saute pan, melt the butter over medium-low heat. Cook the butter to a dark-brown color, about 5 minutes; the darker the color, the nuttier the flavor will be, but be careful not to burn the butter. When the butter is browned, remove it from the heat. Place a whisk in the bowl with the egg mixture and carefully pour in the butter. Having the whisk in the bowl helps prevent the mixture from splattering. Whisk until combined and set aside.
Step 4Divide 1 cup of blueberries among the 6 tart shells, spreading them evenly; there should be room between the blueberries. Carefully pour the browned-butter mixture over the berries. Bake for 45 to 50 minutes, until the crust is a deep golden brown. (If making a 9-inch tart, bake for 1 hour.) Allow the tarts to cool and remove from the rings. Place each on a serving plate.
Step 5In a small pan, combine the sugar and water. Bring to a boil. Remove the syrup from the heat and add the remaining blueberries, swirling the mixture quickly. As soon as the blueberries turn dark blue, about 1 minute, immediately pour them into a strainer.
Step 6Spoon the blanched blueberries on top of the tarts. Sprinkle with powdered sugar. Serve with whipped cream, creme fraiche or ice cream, if desired.