Parisian Gnocchi

Directions

1. 1
   1. To make the pate a 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. 2
   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. 3
   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.
4. 4
   4. Decrease the heat to low and cook the mornay for 6 minutes, stirring frequently, or until the sauce is about as thick as a milkshake. Remove from heat and add the salt, cayenne, and 1/2 cup (40g) of the Swiss-style grated cheese; stir until the cheese is melted.
5. 5
   5. Butter a shallow 2 1/2- to 3-quart (2.5 to 3l) baking dish. (A wide dish is preferable to a deep one for browning the cheese topping.) Sprinkle half of the Parmesan over the bottom and sides. Spread 1 cup (250ml) of the mornay sauce over the bottom of the baking dish.
6. 6
   6. Line a large dinner plate with a few layers of paper towels. Bring a pot of salted water to a low boil. Either using two soupspoons-one to scoop up some of the dough and the other to scrape it into the boiling water-or a spring-loaded ice cream scoop filled partially full, scoop a round of the dough-about 1 generous tablespoon each-and drop it into the water. (The ice cream scoop was a little newfangled for Paule, although she did agree-reluctantly-that it was more expedient and made nicer gnocchi.) Working in batches, poach 8 to 10 gnocchi at a time. Let them poach for 2 minutes, then retrieve them from the water and drain them on the paper towels. (They won't be fully cooked inside.) Repeat, poaching the rest of the gnocchi the same way.
7. 7
   7. Preheat the oven to 350°F (180°C) with the oven rack in the top third of the oven.
8. 8
   8. Once the gnocchi are parcooked, place them in a single layer on top of the mornay in the baking dish, and then spoon the rest of the mornay over the gnocchi in a fairly even layer. Sprinkle the remaining 1 1/4 cups (100g) of Swiss-style cheese over the top, along with the remaining Parmesan. Put the baking dish on a foil-covered baking sheet and bake for 15 minutes. Increase the oven temperature to 400°F (200°C) and bake for another 15 to 20 minutes, until the cheese on top is well browned. Let cool a few minutes, and then serve in the baking dish, family style.