Bubble and Squeak with Ham



2 tablespoons bacon fat
2 tablespoons butter
½ pound onion large diced
½ pound trimmed Brussels sprouts, cut in half the long way and then sliced (leftover cooked Brussels sprouts may also be used)
2 teaspoons minced garlic
½ pound leftover ham, cut into small cubes
1 pound leftover cooked boiled or mashed potatoes