Briefly mix butter and apple flakes in a planetary mixer fitted with a paddle. Add egg yolks and vanilla, mixing until combined. Mix in oat flour and salt on low until combined in a dough. Scoop 1⁄2 of dough onto a well-floured surface and  flatten into a rectangle with rolling pin to 1/4″ Place on large cookie sheet. Roll out other half of dough in the same way as the first. Scoop and spread 38° Brix Apple Purée evenly onto rolled out dough that is on the cookie sheet. Place second half of dough over top of filling and pinch dough in carefully on all sides avoiding air pockets. Bake for 25 – 30 minutes at 325 ̊ F. Cool and cut into 2″ squares.