Place the blueberries, maple syrup, vanilla extract, and lemon juice in a small saucepan over medium low heat. Allow to simmer, then reduce heat to low. Stir occasionally and cook until blueberries are thickened into a sauce.

Meanwhile, butter the outsides of the bread slices. Place grated fontina cheese on one slice of bread.

When blueberry sauce is ready, spoon onto the bread over the cheese.

Cook over medium in a pan for a few minutes on each side until browned. Immediately enjoy while it's hot!