Which type of butter does the recipe call for?

Useful to know

King Arthur explains why the type of butter matters in baking. Salt, fat content and additional processing can affect behaviour even when products share the name “butter”. [1]

Check whether the recipe requires unsalted butter and whether it should be cold, softened or melted. Do not substitute an arbitrary spread just because it is used on bread. To compare attempts, use the same product and measuring method. Otherwise, a change attributed to technique may actually come from different proportions of fat, water and other ingredients.