Make the cream sauce. Melt the butter in a medium frying pan over medium-high heat. Add the onion and garlic, and cook for 1 minute. Sprinkle the flour over the onion mixture and cook, stirring frequently, for 3 minutes. Stir in the half-and-half. Cook the mixture, stirring slowly and continuously, until the sauce comes to a boil and thickens enough to coat the back of the spatula, about 5 minutes. Reduce the heat to low and continue cooking until the sauce is thickened, about 2 minutes more.