Many recipes call for heavy cream as a thickening agent that also adds flavor and richness to sauces, soups and desserts. Half-and-half is a lower-fat alternative to heavy cream. It averages 12 percent butterfat versus 38 percent butterfat in heavy cream. Because it contains less fat, it can't be thickened by whipping or by straight reduction because it will curdle before it thickens. However, half-and-half can be thickened by adding it to a roux, which is a mixture of flour and fat.
Melt butter in a saucepan over medium heat. Gradually pour an equal amount of flour into the melted butter while stirring to thoroughly combine both ingredients.
Cook the roux for about 10 minutes. Stir constantly so that the flour cooks completely but the roux doesn't burn. The roux is ready when the ingredients resemble a smooth paste and the raw flour taste is gone. This is called a blond roux and has a slightly nutty flavor.
Pour cool or room-temperature half-and-half into the roux paste a little at a time to keep the mixture from forming lumps. Stir constantly until you've added all of the half-and-half.
Cook the mixture over medium heat and continue stirring for about 10 minutes or until the half-and-half has thickened. Allow the thickened half-and-half to cool before adding it to soups or sauces. Store any that is left over in the freezer.