1. Preheat the oven to 375°. In a food processor, combine 2 cups flour, 1 tablespoon sugar and the salt. Scatter 1½ sticks of the cubed butter evenly around the blade and pulse a few times, allowing large clumps of the butter to remain. Drizzle ⅓ cup of ice water over the mixture while pulsing to create a loose dough. Remove the dough from the processor and place in the middle of a large piece of plastic wrap. Gather the plastic around the dough, press it together to form a ball and refrigerate for 1 hour.

2. In a medium bowl, whisk together the remaining 3 tablespoons flour, ¼ cup sugar and the almonds. Set aside. Split the rhubarb stalks in half down the middle and cut them into 1½-inch lengths.

3. On a lightly floured work surface, roll the rested dough out in a 15-inch circle, about ⅛-inch thick. Carefully transfer the dough to a baking sheet and spread the reserved almond flour evenly in the middle, leaving 4 inches on all sides of the dough. Mound the rhubarb on top of the almond flour and gently fold the sides of the dough up around the edges of the rhubarb, piecing the dough together to avoid leaving any holes in the edges. Sprinkle the remaining ⅔ cup sugar and the remaining butter cubes over the rhubarb. Bake for 1 hour and 30 minutes, rotating the galette halfway through, until the bottom and edges of the crust are golden brown.

4. In a small bowl, whisk the preserves with the remaining 1 teaspoon ice water and Cognac. Use a pastry brush to generously brush the liquid all over the edges of the galette. Place the galette back in the oven and bake for about 2 minutes longer, until a glossy finish forms on the crust.
5. Let the galette cool on the baking sheet for 5 minutes, then transfer to a cooling rack and let cool completely, about 20 minutes. Serve with sweetened crème fraîche, if desired.