In a stand mixer, combine sourdough discard, instant yeast, and warm water. Let sit 5 minutes until bubbly.
Add salt and slowly mix in the flour using the dough hook on low speed. Knead until dough is smooth, about 5–10 minutes.
Place dough in a large oiled bowl. Cover with a damp tea towel or plastic wrap. Let rise in a warm spot for 2 hours, until doubled.
Coat a cast iron skillet or baking pan with oil. Press dough into the bottom of the pan.
Rub oil on your fingertips and dimple the top of the dough. Drizzle with 1 tablespoon of oil.
Cover and let dough rest another 1–2 hours in a warm spot for the second rise.
Preheat oven to 400°F.
Spread marinara sauce over the dough, then add cheese and toppings.
Bake for 30–35 minutes or until the crust is golden brown and the cheese is bubbly.
Cool for 5–10 minutes on a wire rack before slicing and serving.