Preheat the oven to 400 degrees.

In a cast iron skillet, heat the butter over medium heat until melted.

Add the onions and cook over medium heat for 15-20 minutes stirring occasionally until the onions have turned brown and have caramelized.

While the onions caramelize, place the thawed bread dough on a lightly floured surface. With a rolling pin, roll the dough out into a 12 inch by 12 inch square.

After the onions have caramelized add to the pan the spinach, garlic, and roast beef. Cook until the spinach has wilted. About 3-5 minutes.

Using a slotted spoon, spread the roast beef mixture over the bread dough. Pour out the excess butter and juices from the pan, reserving only about 1 Tablespoon in the bottom.

Sprinkle the grated cheese over the the dough.

Starting at one end, roll the dough up and pinch to seal the edge. Slice the dough into 1 inch pieces and place into the skillet.

Bake at 400 degrees for 25-30 minutes.

Serve warm.