• Combine water, milk, butter and egg yolks, beating well.
• Gently stir in your flour and sea salt.
• Knead the dough on a floured surface for approx. 2 minutes until it is smooth and soft.
• Divide the dough in two, and place the dough in a lightly oiled bowl; cover, and let it rest for at least 30 mins.

While the dough rests, you can work on your filling, which is very straightforwardSauté the finely chopped onions in 1 tablespoon of butter.

• Add to mashed potatoes, then stir in your cheese.
• Season to taste. Set aside to let the potatoes cool.

Back to the doughRoll out the dough to flatten it - approx. 1/8 inch thick.

• Use a round cutter or glass, 3 inch in diameter, to cut out your circles.
• With the leftover dough, knead it and roll it out, and repeat the cutting process.
• Do this until you are out of dough.
• Fill the dough circles with approx. 1 teaspoon of potato mixture by placing it into the centre of the dough circle.
• Pinch the ends very tightly to ensure that the dough is sealed.
• As you go, place the pierogi on a large clean towel. You can cover them to prevent drying while they sit out.
• Bring a large pot of salted water to a boil.
• Place approx. 10 pierogi into the water at a time. Stir to prevent sticking. Once they float to the top, you know they are cooked.
• Remove with a slotted spoon and transfer to a casserole dish. Drizzle some melted butter over the pierogi, cover, and toss very gently to coat the pierogi evenly. This will prevent them from sticking together.
• Serve with sour cream and preferred garnishes.