Combine flour, sugar, and salt in a food processor, then pulse in the cold butter cubes until the mixture resembles coarse peas with some pea-sized butter pieces still visible—this creates the flaky texture we want. Add ice-cold water a little at a time, pulsing just until the dough comes together without becoming wet or overworked. Shape the dough into a disk, wrap it in plastic wrap, and refrigerate for at least 30 minutes while you prepare the other components. I always use ice-cold water because even a few degrees of warmth can prevent the butter from creating those beautiful, crispy layers.

Slice the rhubarb on a bias into 1/2-inch thick pieces—the angle cuts expose more surface area which helps them cook evenly and caramelize beautifully. Toss the rhubarb with sugar and orange zest in a bowl, then let it macerate while you work on the frangipane. The sugar will draw out the rhubarb's juices and the orange zest will brighten the tart flavor of the fruit.

Combine almond flour, sugar, salt, and room-temperature butter in a food processor and blend until the mixture is pale and creamy, then add the egg and vanilla and almond extract, pulsing until completely smooth. The room-temperature butter is crucial here because it creams properly with the almond flour to create a light, luxurious filling—cold butter won't incorporate as well. Transfer to a small bowl and set aside.

Preheat your oven to 400°F. Remove the chilled dough from the refrigerator and roll it out on a lightly floured surface into a 12-inch round about 1/8-inch thick. Transfer the dough to a parchment-lined baking sheet and chill it in the refrigerator while you finish assembling—this prevents shrinkage during baking.

Remove the dough from the refrigerator and spread the frangipane cream from Step 3 evenly over it, leaving a 2-inch border all around the edge. Arrange the macerated rhubarb pieces and their juices on top of the frangipane in a slightly overlapping pattern, then fold the dough edges up and over toward the center, creasing and overlapping as you go—it's okay if some rhubarb peeks through, that's the rustic charm of a galette. Brush the folded dough edges with melted butter and sprinkle generously with coarse demerara sugar, which will caramelize and create a beautiful crunchy texture.

Bake the galette at 400°F for 35 minutes, until the crust is deep golden brown and the rhubarb is tender and bubbling slightly at the edges. Remove from the oven and let it rest on the baking sheet for 10 minutes before serving—this allows the almond cream and fruit to set slightly so slices stay intact. I like to use Kerrygold butter for brushing the crust because its higher fat content gives the deepest, most luxurious golden color.

Slice the galette into wedges using a sharp knife (dipping it in hot water between cuts helps prevent the crust from cracking). Serve warm or at room temperature, optionally garnished with fresh mint leaves and accompanied by vanilla ice cream if desired.