Step 1
Sprinkle yeast and brown sugar over warm water in the bowl of a stand mixer fitted with a dough hook. Let stand 5 to 10 minutes until the yeast softens and begins to form a creamy foam.
Step 2
Turn mixer to the lowest setting and slowly add 2 cups flour 1/2 cup at a time. Add garlic salt and 1/4 cup butter. Integrate remaining 2 cups flour and knead until dough is smooth and elastic 5 to 7 minutes.
Step 3
Coat a large glass bowl with 1 tablespoon grapeseed oil. Shape dough into a ball and place in bowl turning to coat all sides with oil. Spray a piece of plastic wrap with cooking spray and loosely cover bowl. Cover bowl with a towel and let rise in a warm area until dough has doubled in size about 45 minutes. Punch down dough and allow to rest for 20 minutes.
Step 4
While dough is resting heat a skillet over medium heat; cook and stir bulk sausage until browned and crumbly about 5 minutes. Transfer cooked sausage to a bowl with a slotted spoon retaining drippings in the skillet. Fry Italian sausage link in drippings until browned and no longer pink in the center about 10 minutes. Slice sausage.
Step 5
Preheat oven to 400 degrees F (200 degrees C). Grease a 12-inch cast iron skillet with 2 tablespoons grapeseed oil.
Step 6
Press dough into and up the sides of the prepared skillet. Poke holes in dough with a fork to prevent air bubbles. Spread pizza sauce around the base of the crust. Sprinkle 1/3 cup mozzarella cheese over sauce; layer half the bulk sausage half the sliced sausage and half the pepperoni over cheese. Repeat the layers of meat. Top with remaining 1/3 cup mozzarella cheese.
Step 7
Bake in preheated oven on the bottom rack until crust is golden brown about 25 minutes. Brush crust with 1 tablespoon butter; season with Italian seasoning and garlic powder. Remove pizza from skillet and let rest for 3 to 5 minutes before slicing.