1. Preheat the oven to 400°F (200°C). Bring the butter and ½ cup water to a boil in a medium saucepan. Remove from the heat and quickly beat in the flour and salt with a wooden spoon. Return to very low heat and stir until the dough is smooth and very lightly films the bottom of the pan.

2. Remove from the heat and cool 5 minutes. Gradually stir in the beaten egg until the dough is glossy and thick. Stir in the cheese.

3. Butter and flour a baking sheet. Using 2 dessert spoons, drop 16 balls of the dough, spaced well apart, on the baking sheet. Bake for 20–25 minutes, or until puffed and golden.

4. Remove from the oven and use a sharp knife to make a slit in the side of each puff to allow the hot steam to escape. Transfer the puffs onto a wire cake rack and let cool.

5. For the filling, mix the ingredients until combined. Split each puff open and fill with a teaspoon of the mixture. Serve at room temperature.