In large saucepan, melt butter. Cook onion in better over medium-low heat, stirring frequently, until deep golden brown, 20 to 25 minutes. Stir in flour. Cook and stir 5 minutes longer. Sprinkle 1 tbsp. of cheese into each of four (10 to 12ozs. each) ovenproof bowls. Layer: 1/4 of the onion mixture over cheese in each bowl. Combine milk, eggs, bouillon and garlic powder. Stir until bouillon dissolves. Pour about 3.4 cup milk mixture over onions in each bowl. Set bowls in large baking pan on oven rack. Pour very hot water into pan to within 1/2-inch of top of custard. Bake in preheated 375?F oven for 20 minutes. Sprinkle 1 tbsp. of remaining cheese on each of the custards. Continue baking until knife inserted near center comes out clean, about 10 to 15 minutes longer. Remove immediately from hot water. Serve hot.