Caramelized Onion Cheese Pizza with gruyere

1 large onion , very thinly sliced 1/4 teaspoon sugar salt , pinch 4 teaspoons spicy brown mustard 3 teaspoons horseradish 2 teaspoons honey 8 slices light[...]

1 tablespoon olive oil 8 cups sliced yellow onions (about 2 lbs) 5 cups sliced shiitake mushroom caps (about 10 oz whole mushrooms) 4 garlic cloves , minced 2[...]