Heat the oven to 300°F with a rack in the middle position. Mist a 9-inch tart pan with removable bottom with cooking spray and place on a baking sheet. To make the crust, in a food processor, combine both flours, the sugar and salt; process until combined, about 5 seconds. Scatter the butter pieces over the dry ingredients and pulse until the mixture resembles coarse sand, 10 to 12 times. Add the egg yolk and vanilla, then process until the mixture is evenly moistened and cohesive, 20 to 30 seconds; the dough may not form a single mass.