Kek asks: If I would like to substitute butter for oil in a cake recipe (whether it be from scratch or a box mix), how do I do a proper measurement conversion from working with oil to working with butter?
Baking S.O.S. says: Butter measures the same (by volume and by weight) regardless of what form it is in: cold & solid, softened to room temperature, or melted. So, if you would like to replace the oil in a recipe with butter, it is an even exchange. For example: If the recipe calls for 1/2 Cup of oil, simply substitute 1/2 Cup of butter. (or 4 ounces)
The NEXT question becomes: What form should the butter be in when substituting butter for oil? Here is where it helps to explain a little bit about mixing methods. Regardless of the recipe (cookies, cakes, muffins, etc.), the mixing methods fall into just a few basic categories.
The CREAMING METHOD is used when a recipe calls for room temperature butter. When using the creaming method, the procedure is to beat the butter & sugar together on medium speed for 8-10 minutes to incorporate air, which helps the product rise and creates a tender, fluffy texture. (often used with cookies)
When a recipe calls for liquid fat (such as oil or melted butter), the mixing method used is called the MUFFIN METHOD (often used for muffins, as the name implies). In this method, ingredients are usually mixed just until well combined. Less air is incorporated, and the finished product is usually more dense. So. . . if the cake recipe (regardless of whether is is made from scratch or a box mix) calls for oil and you would like to substitute butter, I would recommend melting the butter so you have a liquid fat. Use the muffin method, where ingredients are mixed very little, just until combined. I hope that answers your question!