Preheat oven to 425°F (220°C).
In a saucepan, bring butter, water, and salt to a boil.
Add flour all at once and stir vigorously until mixture forms a ball.
Remove from heat and let cool for 5 minutes.
Add eggs one at a time, beating well after each addition.
Drop by tablespoonfuls onto a baking sheet.
Bake for 20-25 minutes or until golden brown. Let cool.
For the filling, whip heavy cream, sugar, and vanilla extract until stiff peaks form.
Cut puffs in half and fill with whipped cream.