These homemade goldfish crackers are awesome - you can enjoy the salty, crispy goodness without all the sugars and preservatives. Perfection! You'll need a tiny goldfish-shaped cookie cutter, or a different shape cutter of similar size.
Stir the cheese, flours, Cheddar powder, salt, baking powder, and onion powder together in a large bowl until the cheese is evenly distributed and coated. Add the milk and vegetable oil and continue to stir with a spatula, then knead in the bowl with your hands until a cohesive dough forms. It will be crumbly at first, but continue to press and knead the dough until any dry bits are incorporated.
Transfer the dough to your work surface, cover with the upside-down bowl, and let rest for 10 minutes.
Preheat the oven to 375°F (190°C). Line 2 baking sheets with parchment paper or Silpat liners.
Divide the dough into 2 pieces. Refrigerate one piece while you roll the second piece as thin as humanly possible, no more than 1/8-inch thick. (The thinner your dough, the crispier your crackers will be; thicker dough means puffier, more bread-like crackers.)
Stamp out cracker shapes with your cookie cutter of choice: a fish is the traditional shape, of course, but the crackers taste just as good as hearts, stars, circles, or small squares. Transfer the shapes to the prepared baking sheets.
Bake for approximately 15 minutes, until the crackers are crispy and just turning golden at the edges. The timing will vary according to the size and shape of your crackers.
Transfer to a wire rack and let cool completely.
The crackers will soften when kept in an airtight container, so they’re best eaten within a day or two.