Step 1: Prepare the Choux Pastry

• Preheat your oven to 200°C (400°F) and line a baking tray with parchment paper.
• In a medium saucepan, combine water, butter, and a pinch of salt. Heat over medium heat until the butter melts and the mixture begins to boil.

Step 2: Add the Flour

• Remove the saucepan from the heat and add the flour all at once. Stir vigorously with a wooden spoon until the mixture forms a smooth ball and pulls away from the sides of the pan.

Step 3: Incorporate the Eggs

• Let the mixture cool slightly, then beat in the eggs one at a time, mixing thoroughly after each addition. The dough should be smooth and glossy.

Step 4: Add the Cheese and Seasoning

• Stir in the grated cheddar, Parmesan, black pepper, and Dijon mustard (if using). Mix until evenly combined.

Step 5: Pipe or Spoon the Dough

• Transfer the dough to a piping bag fitted with a large round tip, or use a spoon to drop small mounds of dough onto the prepared baking tray, spacing them evenly.

Step 6: Bake the Cheese Puffs

• Bake in the preheated oven for 20-25 minutes, or until the puffs are golden brown and crisp. Avoid opening the oven door during baking to ensure they puff up properly.

Step 7: Serve and Garnish

• Remove from the oven and let the cheese puffs cool slightly on a wire rack. Garnish with chopped chives or parsley before serving.