Prepare the Choux Pastry: In a saucepan, heat water, butter, and salt until boiling. Add flour and stir continuously until the dough pulls away from the sides. Remove from heat and let cool slightly.
Incorporate Eggs: Add eggs one at a time, mixing well after each addition, until the dough is smooth and glossy.
Bake the Shells: Pipe small rounds of dough onto a baking sheet and bake at 375°F (190°C) for 25-30 minutes, until golden and puffed.
Prepare the Lemon Filling: In a saucepan, whisk together lemon juice, zest, sugar, and egg yolks over low heat. Cook until thickened, then remove from heat and stir in butter and marshmallow fluff.
Assemble the Cream Puffs: Slice the cooled pastry shells in half, fill with the lemon mixture, and dust with powdered sugar.
Serve and Enjoy: Optionally, top with a dollop of whipped cream for extra indulgence!