Versatile soup bases are seasoned pastes that add a big boost of concentrated flavor, similar to bouillon granules but much grander in taste.
Melt 1/4 cup butter in a heavy saucepan over low heat; whisk in flour and chicken soup base until smooth. Cook, whisking constantly, 1 minute. Gradually whisk in 1 1/2 cups milk; cook over medium heat, whisking constantly, 3 to 5 minutes or until mixture is thickened and bubbly. Remove from heat, and whisk in Colby-Jack cheese, horseradish, and pepper, whisking until cheese is melted.