Line 2 baking sheets with parchment paper. If serving immediately preheat the oven to 400 degrees. Arrange racks in upper ⅓ and lower ⅓ of the oven.

Assemble all your ingredients so you can mix them quickly as needed.

In a large saucepan, combine the water, butter, salt and mustard, if using. Bring to a boil over medium high heat and stir to melt the butter. Reduce the heat to medium low.

Remove the pan from the heat and add the flour all at once. Stir quickly with a wooden spoon until mixture is well blended.

Return the sauce pan to the burner (now on medium low) and stir for 3-5 minutes until the dough pulls away from the sides of the sauce pan and a film forms on the bottom of the pot. It should be shiny and stiff enough for the spoon to stand up in.

Take the sauce pan off the heat. Beat the dough with an electric hand mixer for about a minute until it stops steaming.

While beating add in the eggs in 4 stages. Beat after each addition until the egg is absorbed and the dough is smooth. Scrape down the sides of the pot periodically with a spatula. After the last addition the dough should be very smooth and creamy looking. Add the cheese and beat til well incorporated.

To Serve Immediately - With a Tablespoon, scoop out the dough and drop as a rounded mound onto the parchment paper lined baking sheets about 1 inch apart. Bake 10 minutes at 400 degrees, then reduce heat to 350 and bake another 20 minutes. Rotate baking sheets top to bottom and front to back half way through. They will feel light and hollow when they are done. Allow to cool slightly and serve warm or at room temperature.

To Freeze- With a Tablespoon, scoop out the dough and mound on parchment lined baking sheets. Place them close together but not touching. Cover the pan with plastic wrap and freeze until solid. (about 4 hours). Transfer frozen gougères to a sealed container or bag and freeze for up to 3 months. To serve heat oven to 450 degrees. Position racks in top ⅓ and bottom ⅓ of the oven. Place frozen gougères on parchment lined baking pans about 1 inch apart. Bake 5 minutes at 450 degrees, then reduce heat to 350 degrees and bake another 25 minutes. Rotate sheets top to bottom and front to back half way through. They will feel light and hollow when they are done. Allow gougères to cool and serve warm or at room temperature.