Preheat the oven to 350ºF (177ºC) and line a rimmed sheet pan with parchment paper.
Add the sourdough discard to a medium-sized bowl, and stir in the melted butter (or olive oil) until completely combined.
Spread the mixture into a very thin rectangle, spread it out as thin as you can with a silicone spatula or offset spatula.
Sprinkle on some salt and/or the flavorings of your choice (everything seasoning, parmesan, garlic powder, rosemary, etc).
Bake in the preheated oven for 10 minutes, then remove and use a pizza or pastry wheel to score into crackers (about 1 ½” long, 1” wide).
Return to the oven and bake for an additional 20-30 minutes, or until crispy and cooked through (note: crackers will crisp up as they cool). If your oven runs hot, start checking them around the 15 minute mark. My oven is calibrated and 30 minutes is perfect, but not everyone has a calibrated oven. Allow to cool to room temperature before transferring to an airtight container. Stores at room temperature for 7-10 days. Recrisp in the oven if needed.