Cheesy Potato Gratin

1/4 cup butter 1/2 stick, or half olive oil and half butter 1 pound mushrooms white or cremini, sliced 1 tablespoon garlic minced 4 cups leeks thinly sliced[...]

2 lbs idaho potatoes (peeled and thinly sliced) 1/2 teaspoon salt 1/2 teaspoon white pepper 1/4 cup snipped chives (fresh) 1/4 minced onion 1 1/2 cups blue[...]

1 tablespoon unsalted butter 1 shallot , finely chopped 2 tablespoons all-purpose flour 1/2 cup chicken stock 1/2 cup heavy cream 1 cup grated gruyere cheese[...]