Sweet Potato and Gouda Gratin
Ingredients:2 pounds deep orange sweet potatoes (3 or 4 medium total), peeled and sliced 1/8 in. thick1 large shallot, thinly sliced, rings separated2 teaspoons chopped fresh thyme leaves, plus a thyme sprigAbout 1 tsp. kosher saltAbout 1/2 tsp. pepper2 cups (6 1/2 oz.) shredded aged gouda cheese4 tablespoons flour, divided3/4 cup whipping cream3/4 cup reduced-sodium…