Corny Grilled Cheese - Jill's Kitchen

Ingredients

• 1 tbsp unsalted butter
• 1/2 cup minced yellow onion
• 1 1/2 cup corn kernels ((from 3 to 4 ears))
• granulated sugar (optional) (if you think the corn needs it)
• 2 tbsp mayonnaise (plus more for brushing)
• 8 oz low-moisture mozzarella (shredded (2 cups))
• 4 oz fontina or provolone cheese (shredded (1 cup))
• 2 tbsp minced flat leaf parsley
• Kosher salt and freshly ground pepper
• 8 slices really good sourdough bread (cut 3/4 inch thick)