In a large mixing bowl, combine the all-purpose flour, fine sea salt, garlic powder, and onion powder. Whisk briefly to combine.

Add the cold, cubed butter to the flour mixture. Using a pastry blender or your fingertips, cut the butter into the flour until the mixture resembles coarse crumbs with some pea-sized pieces of butter remaining.

Stir in the finely shredded sharp cheddar cheese until evenly distributed.

Pour in the sourdough discard. Mix with a spoon or your hands until a shaggy dough forms. If the dough seems too dry and isn't coming together, add 1-2 tablespoons of cold water, a little at a time, until it forms a cohesive ball.

Transfer the dough to a lightly floured surface and gently knead for 1-2 minutes until smooth. Flatten the dough into a disc, wrap tightly in plastic wrap, and refrigerate for at least 30 minutes (or up to 2 days). This chilling step is crucial for easy rolling and flaky crackers.

Preheat your oven to 350°F (175°C). Line two large baking sheets with parchment paper.

Divide the chilled dough in half. On a lightly floured piece of parchment paper (or directly on your baking sheet), roll out one half of the dough very thinly, about 1/16 to 1/8 inch thick. The thinner you roll, the crispier the crackers will be.

Using a sharp knife or a pizza cutter, trim the edges to form a rectangle. Then, cut the dough into squares, rectangles, or any desired cracker shape. You can use a small cookie cutter for fun shapes.

Carefully transfer the cut crackers to the prepared baking sheets, leaving a small space between each one. Gather any scraps, gently re-roll, and cut more crackers until all dough is used. Prick the center of each cracker once or twice with a fork to prevent puffing.

Sprinkle lightly with flaky sea salt, if desired.

Bake for 15-20 minutes, or until the crackers are golden brown and crisp. Baking time may vary depending on cracker thickness and oven. Keep a close eye on them, as they can go from perfectly baked to burnt quickly.

Once baked, remove from the oven and transfer the crackers to a wire rack to cool completely. They will crisp up further as they cool.