In a large cast iron skillet set over medium-low heat, melt 1/2 tablespoon butter. Add the onion, season with salt and pepper and cook, stirring often, until soft and golden, about 20 minutes. Remove to a bowl and set aside.

In the now-empty skillet, melt 2 tablespoons butter over medium-low heat. Add the peppers and mushrooms, season with salt and pepper, and cook until tender. Remove to a bowl and set aside.

Turn the heat up to high. Add 2 more tablespoons of butter to the empty skillet. Once the butter is melted, add the slices of steak. Season with salt and pepper. Cook for only about 45-60 seconds per side. Remove to plate. Once the steak is cooled, cut it into small, bite-sized pieces.

In a small saucepan over medium-low heat, melt the butter. Whisk in the flour; cook for 1-2 minutes or until bubbly and smooth. Slowly whisk in the milk and cook, stirring constantly, until thick and bubbly, about 2-4 minutes.

Remove from heat and vigorously stir in the cheeses and salt & pepper. The sauce will be very thick. Taste and adjust seasonings if needed. Set aside.

Preheat your oven to 450 degrees F. Once the oven is hot, place a pizza stone in the oven to preheat while you're making your pizza.

In a large mixing bowl, whisk together the flour, yeast, sugar and salt. Add the warm water and oil. Mix together until well combined, about a minute. Gradually add 1/2 cup flour until the dough forms a ball. Add more flour if needed.

Dump the dough out onto a floured surface (dough will be somewhat sticky). Knead until the dough is smooth and elastic, about 4 minutes. Add additional flour as needed.

Roll the dough out to a 12-13" circle on parchment paper. Spread the cheese sauce all over the dough. Top with the veggies and meat. Sprinkle the cheese on top.

Transfer pizza to preheated stone and bake for about 10 minutes, or until the crust is nicely browned and the cheese is melted.