In a food processor (or mixing bowl), add the flour and cubed cold butter. Pulse until the butter and flour form pea-sized pieces. If not using a food processor, cut the cold butter into the flour with a fork and knife or a pastry blender.

Add the cold sourdough discard, cold egg yolk (save the white to brush the crust before baking), salt, sugar, and vinegar.

Pulse until just combined — you'll see butter and egg specks throughout, and that's good. We don't want a fully incorporated dough here; those butter pockets melt in the oven for a super flaky crust. If you think it isn't mixed enough, it probably is!

Turn the dough onto a floured surface (or floured pastry mat). It will be crumbly — don't expect a solid ball. Gently flatten into a round disk, wrap in cling wrap, and refrigerate at least 15 minutes so it firms up for rolling.

When ready, place the dough on a lightly floured surface, sprinkle a little flour on top, and roll out with a floured rolling pin to about ⅛-inch thick, until it covers your pan with a bit of overhang. Poke holes with a fork and lightly brush with the reserved egg white.

Style the edges to taste and bake according to your recipe. Over filling, this typically takes about 45 minutes at 375°F. Blind-baked, it usually takes about 20–25 minutes at the same temperature — keep an eye on it.