1. Combine water, butter, sugar and salt in medium-size saucepan. Place over medium-low heat to melt butter. Add flour and cocoa powder all at once; stir vigorously with wooden spoon until mixture pulls away from side of pan, 1 minute. Remove from heat.
2. Heat oven to 400 degrees F. Lightly coat baking sheet with cooking spray.
3. Off heat, add eggs, one at a time, to batter in saucepan, beating well with wooden spoon after each addition. Spoon into large pastry bag fitted with a very large plain tip. Pipe 2-inch rounds onto prepared baking sheet, spacing 2 inches apart. Or drop mixture onto sheet by level 1/4 cupfuls.
4. Bake in 400 degrees F oven 40 minutes, until puffed and firm. Cool slightly. Cut off top third of each puff; scoop out soft center from bases. Cool bases and tops on rack.
5. Fill puffs with ice cream; cover with tops. Freeze on baking sheets until firm. Transfer to airtight containers. Freeze for up to 1 week.
6. Place puffs on plates. Let stand 15 minutes. Dust with confectioners sugar. Garnish with mint.