Margarine (Best Option)
1:1 by volume (e.g., 1 cup margarine per 1 cup butter)Margarine is formulated to have a fat and water content similar to butter, which is essential for the aeration and moisture balance in vanilla cake batter. This similarity helps maintain the cake's tender crumb and buttery flavor profile.
When substituting margarine, use it in the same quantity as butter and ensure it is softened to room temperature for proper creaming with sugar. Avoid margarine with high water content as it can affect the cake's structure.
The final cake will be very close in texture and taste to the original, with a slightly less rich flavor depending on the margarine brand, but generally indistinguishable in a vanilla cake context.