Parisian Gnocchi

1. To make the pâte à choux, heat the water, butter, and 1/2 teaspoon of salt in a saucepan over medium heat just until the butter is melted. Dump in all the flour at once and stir the mixture briskly for about 2 minutes, until the dough forms a smooth ball. Remove from the heat and scrape the dough into the bowl of a stand mixer fitted with the paddle attachment. (If you don't have a stand mixer, simply leave it in the bowl.) Let the dough sit for 3 minutes, stirring it every so often to release some of the heat.

2. With the mixer on medium-high speed, add the eggs one at a time, making sure each one is fully incorporated before adding the next. Add the dry mustard and beat until the dough is completely smooth. Cover the bowl with a kitchen towel and set aside.

3. To make the mornay sauce, melt the butter in the saucepan over medium heat. Add the flour and cook, letting the mixture bubble, stirring constantly for 2 minutes, until the paste is thickened. (Don't let it brown.) Gradually whisk in the milk, beginning slowly and stirring constantly to avoid lumps.