Oil can be substituted for butter in many types of baked goods, including cookies. Since oil has a higher fat content than butter, substitute 7/8 cup of oil (3/4 cup + 2 tablespoons) for every 1 cup of butter called for in cakes, cupcakes, breads and muffins.
For cookies and bars, use just ½ cup of vegetable oil (or other good baking oil) for every 1 cup of butter called for in the recipe. To get the batter or dough to the proper consistency, add milk alternative, juice or water as needed. I usually end up adding about 1 to 2 tablespoons of additional liquid.
Most dairy-free margarines come in tubs and are slightly softer than stick butter. Nonetheless, they seem to substitute quite well 1:1 for butter in baking, and are good to use when a buttery flavor is desired, such as in my Caramel Apple Oat Bars.
When a firm butter is called for, such as in making biscuits for this cobbler recipe, use an equivalent amount of solid coconut oil or shortening.
Alisa Fleming is a contributing editor to Allergic Living and the author of Go Dairy Free: The Guide and Cookbook for Milk Allergies, Lactose Intolerance and Casein Free Living, and founder of Godairyfree.org.
More Allergy-Free Cooking Advice:
Baking with No Milk or Eggs
Secrets to a Better Buttermilk
Dairy-Free Chocolate
