The ability to substitute an ingredient on the fly often saves the day in the kitchen. You can substitute ingredients effectively if you know the purpose and properties of both the original ingredient and the substitution. Take the oil used in a cake mix, for example. Like all fats, oil helps to keep cakes moist. However, unlike other fats, such as butter or margarine, oil doesn’t add flavor. You can substitute just about any fat for oil in a cake mix and still get the moistness you want, but expect to taste a slight buttery finish when you use oleo, another term for margarine.
Measure an amount of oleo equal to the amount of oil called for in the cake mix and add 1 extra tablespoon. Most cake mixes call for 1/3 cup of oil, so spoon 1/3 cup of oleo into a measuring cup plus 1 tablespoon. Melting removes the air that makes up some of the volume in cold oleo, so you have to melt a bit more for it to equal the same amount of oil.
Scrape the oleo into a saucepan and melt it over low heat. Wipe out the measuring cup with a paper towel.
Pour the melted oleo back into the measuring cup until it reaches the 1/3-cup mark. Allow the margarine to reach room temperature before adding it to the cake mix.