The invention relates to a removable lid for defining a food cooking or heating enclosure (5) in a microwave oven, comprising an outer wall (2) pervious to microwaves and sealed for air and steam, an inner wall (3) pervious for microwaves and adapted for the passage of air and steam, and an intermediate ply (4) made of a porous water-retaining material and provided between the inner and outer walls, characterised in that the outer wall (2) includes at its inner face oriented towards the inner wall (3) at least one convex conformation (10) for defining a cold condensation area, the inner wall (3) being open opposite each convex conformation in order to expose at least the portion of the intermediate ply (4) surrounding the convex conformation (10).