For the dough: Add the flour to a large mixing bowl and make a well in the center. Drop the milk
, salt and egg into the center. Mix with your hands until the dough
sticks together. Wrap in plastic wrap
and chill for 20 minutes. Place the dough on a floured surface and roll out to about 1/8-inch thick. Cut out 12 circles using a cookie cutter
For the filing: Boil the garlic and potatoes and in a large pot of boiling salt water until fork-tender, about 15 minutes. Drain. Mash
together the potatoes, garlic, Cheddar, cream, vinegar, butter, salt, green onions and pepper to taste in a medium bowl.
For assembly and cooking: Place some potato mixture on half of a circle of dough. Fold the other half of the circle over the potato mixture and seal using a fork. Repeat with the remaining dough and filling. Lay out the prepared pierogies on a large baking sheet and cover with a dish towel. Fill a large pot with water and bring to a boil. Drop in the pierogies 4 at a time and cook uncovered until they float
to the surface, about 10 minutes. Drain.
Heat 2 tablespoons canola oil in a pan and sear
the pierogies until golden, about 45 seconds per side.
Mix together the sour cream and gherkins in a bowl.
Heat some canola oil
in a medium pan over medium-high heat. Add the onions and fry
until dark and crispy, 3 to 5 minutes. Drain
Top the pierogies with the fried onion slivers and serve with sweet gherkin sour cream