To make raisin sauce for baked ham, combine 1 cup of water and 1 cup of raisins into a medium-sized saucepan, and bring the mixture to a boil. Mix in 2 tablespoons each of brown sugar and flour. Stir in 2 tablespoons of butter, and cook until the sauce thickens.
After the sauce comes to an initial boil, reduce the heat to medium. Stir the sauce constantly. To prevent the sugar and flour from clumping, mix them together in a separate container. Then, sprinkle the mix gradually over the sauce, 1/2 tablespoon at a time, integrating the dry ingredients fully before adding more.
If you want a rum-raisin sauce to go with baked ham, add 2 tablespoons of rum after you incorporate the butter. Sample the sauce, and add more rum to taste. Add the rum 1 tablespoon at a time, and stir the sauce thoroughly before tasting it.
For a Southern variation on raisin sauce, stir in 1 tablespoon each of dry mustard and vinegar after you add the flour. Replace the flour with cornstarch for a thicker sauce. If your sauce is too rich or heavy, stir in 2 tablespoons of lemon juice and 1 tablespoon of grated lemon zest.