PREPARING THE DOUGH
In a large bowl, whisk the eggs, whole milk, sour cream, kosher salt, and water until combined. Add 4 cups of flour to the bowl. Mix with a wooden spoon until a shaggy dough forms. Knead the dough in the bowl with your hands until the dough starts to stick together. Turn out the dough to a work surface dusted with flour, and continue to knead. Add flour as needed if the dough sticks to the surface.

Knead until smooth and supple. Transfer the dough back to the bowl. Place plastic wrap over the bowl, and let the dough rest for 2 hours

PREPARING THE FILLING
Heat the grapeseed oil in a medium saute pan over medium-high heat. Add the Fullblood Wagyu ground beef to the pan, and season with kosher salt.Cook the beef, while stirring occasionally. Use a wooden spook to break up the beef into small pieces. Cook for about 5 minutes until the meat is browned and cooked through.Transfer the cooked ground beef to a medium bowl.Return the pan to medium-high heat. Add the julienned onion, and season with 1 teaspoon of kosher salt.

Cook for around 10 minutes, while stirring often, until the onion is translucent and browned around the edges.Deglaze with water, and scrape the bottom of the pan. Once water is evaporated, keep cooking for 7 minutes to caramelize the onions. Transfer the onions into the same bowl with the cooked ground beef. Let the beef and onion mixture cool in the refrigerator for 30 minutes. Add the grated smoked cheddar to the bowl, and mix to combine. Season to taste with kosher salt and black pepper.

PREPARING THE FULLBLOOD WAGYU BEEF PIEROGIES
Lightly dust 2 parchment-lined, rimmed baking sheets with cornstarch. Cover the baking sheets loosely with plastic.Using a bench scraper or knife, divide the dough in half.Place one piece of dough on a lightly floured surface. Dust the other piece of dough with flour, and cover it with plastic. On the floured surface, roll out the dough to a thickness of less than an 1/8 inch. Frequently lift up the dough to dust with flour. This will prevent sticking

Working with one batch of pierogies at a time, dip your pastry brush in egg wash, and coat the edges of the dough round. Transfer about 1 tablespoon of the beef, onion, and cheese mixture onto one side of the dough round. Leave the other side of the dough round empty.Grasp the dough round from the empty side, and pull it up and over the filling, while stretching the dough slightly.Press down on the dough to seal the edges together, creating a semicircle.

Dip a fork in flour. Then, crimp the rounded edge with tines of a fork.Transfer the pierogies to prepared baking sheet, tucking them underneath the plastic. Repeat the process with the remaining dough rounds (filling, folding, and sealing them). You should end up with around 40-45 pierogies.

FINAL STEPS
Heat a large pot of salted water (4 quarts of water per 1/4 cup salt) to a boil.Working in batches and using a spider or slotted spoon, gently lower 6–8 pierogies into a large pot of boiling water.Cook for around 2 minutes until the pierogies are wrinkly, slightly translucent, and floating.Transfer the boiled pierogies to a baking sheet to drain. Repeat the process until all of the pierogies have been boiled.Heat 1 tablespoon of butter in a medium skillet over medium heat.

Once it has melted, add in the pierogies to cook, turning once during the cooking process.Cook until the pierogies are golden brown and crisp on both sides - this usually takes about 3 minutes. Transfer the cooked pierogies to a plate. Drizzle them with the remaining butter in skillet, and season lightly with kosher salt.Repeat the process until all pierogies are finished.Serve the Fullblood Wagyu beef pierogies with sour cream, and enjoy!