Margarine (Best Option)
1:1 (1 cup margarine per 1 cup butter)Margarine is formulated to mimic butter’s fat content and water ratio, which is critical for the structure and moistness of brownies. The fat coats flour proteins, limiting gluten formation and promoting tenderness.
For best results, use stick margarine rather than tub margarine to match butter’s solidity and water content. Ensure margarine is at room temperature for even mixing.
Brownies made with margarine will have a very similar texture and flavor to those made with butter, with only a slight difference in richness depending on margarine quality.