Corn kernels packaged within an elongate bag (10) can be popped with microwaves and served in the bag. During popping, part of the bag's longitudinally-extending back seal opens and permits vapors to vent from the bag. After the kernels are popped, the back seal (28) is fully opened to transform the bag (10) into a serving bowl having an opening defined by the edges of bag material previously forming the back seal (28). The bag (10) is made from a laminate of two paper layers (38,40) with a susceptor (36) between the two paper layers (38,40) at a location where the bag (10) will contact the floor of the microwave oven. Alternatively, instead of using two layers of paper, a single layer of paper surrounding a layer of polymeric barrier material can be employed. The back seal (28) is formed from side edges of a web (30,32) of the laminate either by bonding the inner layers of the web edges together or by bonding the inner layer of one web edge to the outer layer of the other web edge. If the innermost layer of the bag is made of a polymeric barrier material, the back seal can be formed by pressing the web edges together under heat and pressure. If the innermost layer is paper, an adhesive must be applied to the web edges before they are pressed together, usually at elevated temperatures. A method of preparing the package of corn kernels is also disclosed.