Make the crust: Position a rack in the center of the oven and preheat to 350ºF. In a stand mixer fitted with the paddle attachment, combine the almond flour, sweet rice flour, oat flour, tapioca flour, sugar, and salt. Scatter the butter pieces over the top and drizzle with the vanilla extract. Turn the mixer to medium-low and run until the dough comes together in moist clumps and the butter is worked through, 3 to 5 minutes. (Alternatively, pulse the ingredients together in a food processor or rub the butter in with your fingertips.)