1. In a pan, melt the butter over low heat.
2. Add the sliced onions and salt. Cook over low heat (don’t burn) until golden brown.
3. Preheat oven to 400F.
4. Combine the olive oil and garlic and brush the flatbreads with the mixture.
5. Add the mozzarella, blue cheese, and some grilled onions (save the rest for another use), and top with diced California prunes.
6. Bake for 10 minutes, or until the cheese is bubbly and beginning to brown.
7. Remove from oven, slice and serve immediately.