- Preheat oven to 425°F. Heat the oil in a medium pan over medium high heat.
- Add the onions and cook until caramelized, about 15 minutes and remove from heat.
- Roll out the dough into a rectangle on a parchment lined baking sheet.
- Spread the Dijon mustard in a thin layer across the top of the dough. Layer the onions, ham, and cheese on top leaving a 1-inch boarder on the edges.
- Roll the dough lengthwise into a tight log, fold the edges under and cut 6-8 slits in the top.
- Brush with the egg wash and bake until golden brown, 45-50 minutes.
- Serve warm.