An improved apparatus and method for uniformly cooking thick layers of food product in a saturated steam environment. A foraminous conveyor belt transports a thick layer of food product into a walled cooking chamber open at its ends. The walls trap pure saturated steam to the exclusion of air in the upper region of the chamber. A pressurized source of cooking energy supplies steam through a network of steam pipes situated just below the level of the belt along its carryway through the upper region of the cooking chamber. The pipes, which span the width of the conveyor belt, include small, restricted openings uniformly distributed along the pipes. The openings form steam outlets. The pipes are oriented with the steam outlets facing the conveyor belt. Saturated steam is emitted through the outlets directed through the foraminous conveyor belt at a velocity great enough to penetrate the thick product layer to cook even the innermost product within the thick layer, thereby improving the uniformity of the cook. The thick product layer slows the steam as it penetrates the layer to prevent the formation of turbulent flow paths that could draw unwanted air into the 212.degree. F. saturated steam cooking region. An S-shaped back-flip in the conveying path repositions the product on the belt to further improve cooking uniformity.