Directions:

In a large nonstick skillet, melt 1 tablespoon of the butter over low heat. Add the onions and cook very slowly, stirring occasionally, until they turn a dark golden color, 30 to 40 minutes. If the onions begin to scorch, add about 1 tablespoon of water. Remove the onions from pan and set aside. Wipe the skillet with a paper towel, but do not wash it. (The onions can be prepared up to 6 hours in advance and kept covered at room temperature.)

Heat the same skillet over the medium-high heat. Add the cumin seeds and toast just until they become fragrant, about 3 minutes (watch carefully, they burn easily). Remove the seeds and let cool briefly. Do not wash the skillet. When the seeds are cool, crush them using a mortar and pestle. Or place them in a reasonable plastic bag and lightly pound with a mallet or the bottom of a heavy skillet. In a medium bowl, toss the crushed seeds with the cheese.

To assemble: Butter one side of each slice of bread with the remaining 2 tablespoons butter. Place 4 slices on your work surface, buttered side down. Distribute the cheese evenly over the 4 slices, followed by the onions. Place the remaining 4 bread slices on top, buttered side up.

Brush the grill rack with oil and preheat the grill to medium-high. Put the sandwiches on the grill(in batches if necessary), cover, and cook for 2 minutes, or until the undersides are golden brown and the cheese has begun to melt. Uncover, and turn the sandwiches with a spatula, pressing firmly to flatten them slightly. Cook for 1 minute or until the undersides are golden brown. Turn the sandwiches again, press with the spatula, and cook for 30 seconds, or until the cheese has melted completely. Serve immediately.