Preparation Position 1 rack in top third and 1 rack in bottom third of oven and preheat to 425°F. Butter and flour 2 large baking sheets. Combine 1 cup water, butter, salt, and pepper in heavy medium saucepan; bring to boil over medium-high heat. Add flour and stir vigorously with wooden spoon until mixture forms smooth ball. Continue stirring until film forms over bottom of saucepan, about 2 minutes. Remove pan from heat. Beat in mustard. Beat in eggs 1 at a time. Beat in cheese. Drop batter by heaping teaspoonfuls onto prepared sheets, spacing about 1 1/2 inches apart; bake 15 minutes. Reverse position of sheets and bake until puffs are golden brown, about 5 minutes longer. Serve hot.
Preparation Position 1 rack in top third and 1 rack in bottom third of oven and preheat to 425°F. Butter and flour 2 large baking sheets. Combine 1 cup water, butter, salt, and pepper in heavy medium saucepan; bring to boil over medium-high heat. Add flour and stir vigorously with wooden spoon until mixture forms smooth ball. Continue stirring until film forms over bottom of saucepan, about 2 minutes. Remove pan from heat. Beat in mustard. Beat in eggs 1 at a time. Beat in cheese. Drop batter by heaping teaspoonfuls onto prepared sheets, spacing about 1 1/2 inches apart; bake 15 minutes. Reverse position of sheets and bake until puffs are golden brown, about 5 minutes longer. Serve hot.