Stir until the dough comes together enough that you can knead it. Knead the dough until it is very smooth and elastic, about 8 to 10 minutes. Separate the dough into 4 equal-sized portions. Form each one into a long rough oval shape, no thicker than 1/2 of an inch and no wider than 3 inches (they can be as long as needed). Seal them tightly with plastic wrap and refrigerate for 1 hour.
In the center between the markings, use the pastry bag to pipe a circle of ricotta filling that's about 2 inches in diameter. Use a spoon to gently transfer one of the egg yolks into the ricotta well. Use the pastry bag to pipe one more circle on top of the initial circle, thus walling-in the egg yolk. Repeat between every marking. Once you have all your filling placed, dip your finger (or use a pastry brush) in a glass of water and gently run it along the exposed pasta dough, re-dipping as-need to keep your finger lightly damp (this will help the dough seal). You don't want a lot of water on the dough, just a trace.
For square ravioli, use a pizza cutter to cut the sheet across into individual raviolo. For round raviolo, you can use a large (4 to 5-inch circular cookie cutter.)
Repeat the above process with the remaining filling and dough until all the ravioli have been assembled.
The ravioli should be enjoyed within 24 hours. These do not freeze well, since the yolk takes on a gelatinous texture when frozen. They will keep in the refrigerator for up to 24 hours, I recommend storing them in airtight rectangular tupperware containers with a sheet of parchment paper that's been brushed with oil between each egg yolk raviolo (to prevent sticking). If you store them any longer than 24 hours, the yolk dampens the dough and makes it extra sticky, which can cause it to tear.
Makes about 10 to 12 individual 4 to 5-inch square raviolis. About 2 ravioli is good for one person, depending on your appetite!
Bring a quart of water to a boil. Add 2 teaspoons of salt and stir to dissolve. Add 2 ravioli and cook 4 minutes for al dente and 5 minutes for a softer pasta, stirring once per minute to keep them from sticking to the bottom of the pot/each other.
Use a slotted or mesh spoon to remove the ravioli from the water and plate it. Garnish with 1/2 cup of the pesto, some grated lemon zest and parmesan, and enjoy!
Disclaimer: Consuming raw or undercooked eggs can result in food born illness.