8 ounces sliced cremini mushrooms
1 tablespoon unsalted butter
1 tablespoon olive oil
3 garlic cloves, minced or pressed
a pinch of salt + pepper
4 slices whole grain bread
6 ounces fontina cheese, freshly grated

mustard aioli
1 1/2 tablespoons dijon mustard
1 large egg yolk
2 teaspoons fresh lemon juice
1/2 cup olive oil
2 tablespoons whole grain mustard
1 tablespoon horseradish
a pinch of salt + pepper