Add the flour, salt, garlic powder, smoked paprika, black pepper, and cold butter to a Magic Bullet cup. Pulse until the mixture resembles coarse crumbs.
Add the shredded cheddar and Parmesan. Pulse several times until evenly combined.
Add 2 tablespoons of ice water and pulse until the dough begins to come together. If needed, add the remaining tablespoon of water, one teaspoon at a time, until the dough holds together when squeezed.
Turn the dough onto a sheet of plastic wrap or parchment paper and press it into a disk. Refrigerate for 20–30 minutes.
Preheat your oven to 375°F.
Roll the chilled dough between two sheets of parchment paper until it's about ⅛-inch thick.
Cut into 1-inch squares using a knife or pizza cutter. Prick each cracker once or twice with a fork.
If desired, sprinkle with flaky sea salt or your favorite seasoning.
Bake for 12–15 minutes, rotating the baking sheet halfway through, until the edges are lightly golden.
Allow the crackers to cool completely before serving. They'll continue to crisp as they cool.