Method

• 1.
  Preheat oven to 220°C/200°C fan-forced. Grease a large baking tray and line with baking paper. Place butter, 1/2 tsp salt flakes and 2/3 cup (165ml) water in a medium heavy-based saucepan over medium-high heat. Cook, swirling pan occasionally, until butter has melted, then bring mixture to the boil.
• 2.
  Immediately add flour and beat vigorously with a wooden spoon for at least 2 minutes or until mixture forms a smooth ball that pulls away from the sides of the pan. Reduce heat to low and beat mixture for at least 1 minute to dry out the dough.
• 3.
  Remove from heat and set aside for at least 1 minute to cool slightly. Add the 3 eggs, one at a time, beating thoroughly with a wooden spoon until combined (dough should be shiny and smooth).
• 4.
  Stir in coarsely grated cheese, mustard and mustard powder. Season with freshly ground black pepper. Transfer choux dough to a piping bag fitted with a 1cm round nozzle. Pipe 20 walnut-shell-sized (roughly 4cm) rounds onto the prepared tray, 3cm apart, to allow enough room for them to double in size.
• 5.
  Lightly beat extra egg for the egg wash. Using your fingertips, gently brush the tops of the gougères with a small amount of egg wash, being careful not to smash them or let any excess egg wash fall onto the paper. Sprinkle tops with extra finely grated cheese. Bake for 20-25 minutes until gougères are puffed, golden and feel light for their size. Stand on tray for 2-3 minutes.
• 6.
  Serve while hot, with Champagne, if desired.