1. Preheat oven to 400 degrees. Line 2 baking sheets with parchment paper; set aside. Put butter, sugar, salt, and 1 cup water into a medium saucepan. Bring to a boil, stirring until sugar has dissolved. Remove from heat. Add flour all at once, and stir until combined. Return to heat; cook, stirring constantly, until mixture pulls away from sides and a film forms on bottom of pan, about 1 minute more.

2. Remove from heat and continue mixing until cooled, 8 to 10 minutes. Add 4 eggs, one at a time, mixing well after each addition. Mix until very smooth.

3. Transfer batter to a pastry bag fitted with a 1/2-inch plain round tip (such as Ateco #806). Pipe a small amount of batter under each corner of parchment to hold it in place on sheet. Pipe remaining batter into 1 1/2-inch rounds (about 3/4-inch high) onto parchment, spacing about 2 inches apart. Whisk together remaining egg with 1 teaspoon water. Gently smooth peaked tops with moistened fingertip; lightly brush with egg wash.

4. Bake 15 minutes. Rotate sheets, and reduce oven temperature to 350 degrees. Bake until cooked through and dry in center, about 20 minutes more. Transfer puffs to wire racks set over parchment paper, and let cool completely.

5. Cut each profiteroles in half horizontally, and fill with 1-ounce scoops of vanilla gelato. Serve topped with raspberry coulis.