Special equipment: Food processor, stand mixer
For the fennel crust: Add the flour, ground fennel and crushed sea salt to a food processor and pulse to combine. Next add the butter and pulse to pebble-size granules. With the food processor running, slowly stream in the cold grape juice -- stop when the dough comes together, even if you haven't added the full 1/4 cup. Remove the dough from the food processor, form into a disc, and wrap with plastic wrap. Refrigerate for at least 2 hours or overnight.
For the grape and ricotta filling: To a stand mixer fitted with the paddle attachment, add the crumbled almond paste, granulated sugar and 1/4 teaspoon of the crushed sea salt. Turn the mixer on low speed and slowly increase the speed to medium-high. Continue to beat the almond paste on high speed for 3 to 4 minutes, until the sugar is completely combined with the almond paste. (The mixture will have softened for the most part, but some of the almond paste will still have the texture of sand.) Add the ricotta, lemon zest, cinnamon, nutmeg and one of the eggs. Beat on medium-high for an additional 3 to 4 minutes, scraping the sides and bottom of the bowl halfway through to ensure the almond paste is completely combined with the ricotta. Set aside at room temperature until ready to use.
Preheat the oven to 400 degrees F. Line a baking sheet with parchment paper.
Remove the rested dough from the refrigerator and let it come to room temperature; this can take anywhere from 30 minutes to over an hour.
Just before rolling out the dough, combine the green grapes, red grapes, honey and the remaining 1/2 teaspoon crushed sea salt in a bowl. Set aside. (Do not let the mixture sit for any length of time or the grapes will release too much liquid.)
On a lightly floured work surface, roll out the dough into a 14-inch round. Roll the crust onto the rolling pin, then unroll it onto the prepared baking sheet; arrange in the center of the baking sheet (the sides will overhang by a couple inches). Using an offset spatula, evenly spread the ricotta frangipane onto the crust, leaving a 2-inch border. Mound the grape mixture (and any honey from the bowl) in the center of the frangipane, leaving at least a 2-inch border of frangipane. Gently fold the sides of the crust toward the center, covering 1 to 2 inches of the grapes. Allow the dough to fold over and land naturally; the galette doesn't have to look perfect, as long as all the sides are folded over to seal the filling inside the dough.
Whisk the remaining egg and brush it generously over the crust. Sprinkle the turbinado sugar over the crust and grapes. Bake for 35 to 40 minutes. When done, the crust will be a deep golden brown, the grapes will have browned slightly but still hold their shape, and the frangipane will look set except for a little bubbling in the center. Let cool.
For the red wine syrup: In a medium saucepan, combine the red wine, granulated sugar and fennel seed. Bring to a boil and cook until reduced to about 3/4 cup, 15 to 20 minutes. Strain the fennel seeds from the syrup and let cool; the syrup will thicken as it cools. If the syrup becomes too thick, stir in warm water, 1 tablespoon at a time, until it reaches the desired consistency. (Makes 3/4 cup.)
To serve: Slice the galette and drizzle with red wine syrup.
For the crust, use a regular store-bought white grape juice, such as Welch's. The sugar in the juice replaces sugar in the crust. For the ricotta, use a store-bought ricotta such as Galbani, which has a lower moisture content than fresh-made ricotta. If you do use fresh ricotta, it may take longer to drain off excess liquid.