Unsalted Margarine (Best Option)
1:1 (1 cup margarine per 1 cup butter)Unsalted margarine is formulated to mimic butter's fat content and melting behavior, which is critical in bread pudding for creating a rich, custardy texture. The fat coats the bread, helping it absorb the custard evenly and preventing dryness.
When substituting, ensure the margarine is unsalted to control overall salt levels in the pudding. Use it at room temperature for even mixing. Margarine's water content can be slightly higher than butter's, so monitor for slight changes in texture.
The final bread pudding will be very close in taste and texture to the original, with minimal flavor difference, making it the most reliable substitute.