Combine brown rice flour, all-purpose flour, cornstarch, coconut sugar, and sea salt in a food processor. Pulse in the cold diced butter until the mixture resembles coarse rice grains—this creates pockets of butter that produce a flaky crust. Add ice water one tablespoon at a time, pulsing gently until the dough just comes together without becoming wet or sticky. Turn the dough onto a lightly floured surface, gently knead it a few times to bring it together, then shape into a disk. Wrap in plastic and chill for at least 30 minutes while you prepare the filling.

Cut rhubarb into 1-inch pieces and place in a bowl with honey, dried culinary lavender, vanilla essence, scraped vanilla bean seeds, and lemon juice. Gently fold in 1 cup of the raspberries, being careful not to crush them. Let the filling sit while the dough chills—this allows the rhubarb to start releasing its juices and the flavors to meld together. I like to leave the filling slightly chunky rather than breaking down the fruit too much, as it keeps the galette from becoming too jammy.

Preheat your oven to 400°F. On a lightly floured surface, roll the chilled dough to about 1/8-inch thickness into a roughly 12-inch circle. Transfer it to a parchment-lined baking sheet. Spoon the rhubarb and raspberry filling from Step 2 into the center, leaving a 3-inch border of exposed dough around the edges. Fold the dough edges up and over the filling, creating rustic pleats—don't worry about perfection; the imperfect folds are part of the galette's charm. Chill the assembled galette for 15 minutes while the oven finishes preheating.

Remove the galette from the fridge and brush the exposed dough edges generously with beaten egg wash. Sprinkle the slivered almonds over the filling and folded crust edges. In a small bowl, mix the remaining 1 tablespoon of dried lavender with the coarse sparkling sugar, then sprinkle 1–2 tablespoons over the dough. Scatter the remaining 1 cup of fresh raspberries and cubed butter over the top of the filling—I add these at this stage so the raspberries stay whole and don't get overcooked. Bake for 45–50 minutes until the crust is deep golden brown and the filling is bubbling slightly at the edges.

Allow the galette to cool for at least 10 minutes on the baking sheet before slicing—this lets the filling set slightly so it won't run all over the plate. Slide it onto a serving platter and serve warm or at room temperature with a scoop of vanilla ice cream on the side. The combination of warm galette and cold ice cream lets each element shine.