1.) Prepare Zinfandel Onions. Heat Olive Oil in heavy bottomed pan. Add onions and cook on medium heat to sweat. Once the bottom of the pan starts to color, turn down heat and continue to cook onions allowing the natural sugars to caramelize. Be patient. Drink a glass of wine. If the bottom of the pan gets to dark or starts to stick add a small amount of water to deglaze pan. Cook the onions until they are a very dark brown to maximize flavor. When you think they are caramelized enough keep cooking darker is better. Add Zinfandel, salt and black pepper and reduce wine until no moisture is left. Set aside to cool.
2.) Pre-heat panini press
3.) Brush one side of each slice of bread with olive oil. Lay the slices oiled side down on a clean work surface. Spread Zinfandel Onions on one side of bread. Arrange the mozzarella and fontina cheese slices on top of onions, then top with the other slice oiled side up.
4.) Place sandwich on pre-heated panini maker and cook according to manufacture’s instructions until golden brown and delicious. About 2 minutes.
5.) Transfer the sandwich to cutting board and cut in half. Serve immediately paired with Zinfandel.