Preheat over to 375° F. Grease a 10 inch tart pan with removable bottom. Bring milk, butter and salt to a boil, stirring contantly. Remove from heat.
Add flour all at once and beat with a wooden spoon until mixture pulls away from sides. Set over low heat and stir for 1 minute. Cool slightly. Add eggs one at a time, beating well after each addition. Mix in 1/2 cup gruyere. Spread batter over bottom of tart pan. Brush top with glaze.
Sprinkle with remaining cheese. Bake until pastry puffs and top is golden brown, about 55 minutes. Cut into wedges (pastry will fall). Serve warm.
Servings: