Cut chunks of Fontina, Goat cheese, & Taleggio into a small mixing bowl. These cheeses should be very soft and, if at room temperature, somewhat easy to mix together. The cheeses will form a large ball once combined. Set aside.
On a nonstick fry pan or griddle, heat your surface to a medium-low heat. It’s key to not overheat so that your cheese will be cooked evenly before your bread is done toasting.
Butter one side of the Sourdough, sprinkle finely grated Parm on the outside, and lightly press the cheese into the bread. Quickly turn the buttered side face down and onto the warm surface.
Take 1/3-1/2 of the mixture and spread onto the exposed side of your sandwich. Take the other slide of bread and repeat the same procedure, buttering one side, pressing finely grated Parm into the buttered side, and putting the butter side (face up) on the top of your sandwich. Wait a couple of minutes for the cheese inside to melt and stick to the top slice of bread.
Once the cheese is somewhat melted and the bottom slice is golden brown, quickly flip your sandwich and cook on the opposite surface. Continue to cook on low to medium heat until the other slide is golden brown on the outside and cheese inside is warm and completely melted. Repeat 2-3 times. Cut in half and serve.
With a whisk mix the olive oil, lemon juice, salt & pepper together. Pour over 2-3 cups of arugula and toss in a mixing bowl.
Heat a 10-12 inch skillet* to medium-high heat. Melt butter and warm olive oil.
After butter/oil mixture is warm (careful not to burn) add onions. Coat onions with butter/oil mixture. Cover with a lid (I used a jelly roll pan because my skillet doesn’t have a lid) for 15 minutes, reduce heat to medium-low.
Stir in 1/4-1/2 cup of water to onion mixture. Cover again and let cook for 40-45 minutes, checking and stirring every 10 minutes or so. Be cautious to watch your onions carefully as you near the end of this step!
Mix in balsamic, syrup, sugar, and salt & pepper. Cook for an additional 10 minutes. Your mixture should be thick (no excess liquid), like a marmalade. This recipe makes 1-2 cups and will stay good for 7-10 days refrigerated.
*This marmalade can be made in a frying pan or sauce pan, but is preferably made in a skillet for optimal flavor and seasoning.