Place the popover pan in the oven. Heat the oven and pan to 350. Gently warm the milk over low heat and set aside. Whisk the eggs until frothy and slowly whisk in the milk (so as not to cook the eggs). Set the mixture aside. Sift the flour with te salt. Slowly add this dry mixture and gently combine until mostly smooth. Once combined, remove the pan from the oven and spray with vegetable spray. While the batter is still slightly warm, fill each popover cup 3/4 full. Top each popover with 2 1/2 tbsp of the grated gruyere. Bake at 350 for 50 minutes rotating the pan 1/2 a turn after 15 minutes of baking. Remove from over, remove from pan and serve immediately.