In a food processor with the blade attachment, add flour, baking powder, sugar, salt, and cubed cold butter. Pulse for about 30 seconds, or until the mixture resembles coarse crumbs.
Slowly add 1/4 cup ice water while pulsing until a dough starts to form. If the dough is too dry, add more ice water 1 tablespoon at a time.
Remove the dough, shape it into a flat disc, and wrap it in plastic wrap. Refrigerate for at least 1 hour (or overnight for best results).
When ready to bake, preheat the oven to 400°F (200°C) and line a baking sheet with parchment paper.
Roll out the chilled dough on a lightly floured surface to about 1/8-inch thickness. Use a small fluted cookie cutter to cut out crackers. Transfer to the prepared baking sheet. Re-roll scraps to use all the dough.
Prick each cracker a few times with a fork to prevent puffing during baking.
Lightly brush the tops of the crackers with whisked egg for a glossy, golden finish.
Bake for 10 minutes or until golden brown.
Let the crackers cool on the baking sheet for about 10 minutes. They’ll crisp up more as they cool. Enjoy!