!The day before:
!For the filling:
Preheat oven to 400!Fdegrees. Wrap sweet potatoes and the head of garlic in aluminum foil and place all three on a large cookie sheet. Bake at 400 degrees for 45-60 minutes, or until the potatoes are soft and the garlic is golden brown.
Remove from the oven, let cool until you are able to handle them easily, then scoop the sweet potato filling into a large bowl. Remove the roasted cloves of garlic from the head and add to sweet potato. Pass this whole mixture through a ricer (or mash with a potato mashed).
Stir in the bacon crumbles, then measure out rounded teaspoons of this filling onto a plate. (This is a super cool tip from the Kitchn that helps speed up the pierogi-making process!)
!For the dough:
Combine flour and salt in a large bowl. In a separate, smaller bowl, whisk together water, egg, and sour cream. Pour this wet mixture over the flour mixture and stir with a large wooden spoon until a rough dough forms.
Turn the dough out onto a lightly floured surface and knead for 6-8 minutes by hand (or with a dough hook for 4-5 minutes). The dough should be smooth and no longer stick to your hands.
Divide it in half and roll the dough out to 1/8 inch thick. Use a 3 inch biscuit or cookie cutter to cut out pierogi circles. Collect the scraps and re-roll to form more circles. Repeat with the other half of dough until all the pierogi circles are cut out.
Place a pierogi circle in the palm of your hand, place one of the teaspoons of sweet potato mixture in the center, then pinch the two farthest sides of the circle together with your fingers. Continue pinching around the outside the circle with your fingers until you completely seal the pierogi, forming a half circle. Repeat with the rest of the pierogi and place on a lightly floured cookie sheet.
Once all pierogi are formed, either freeze until firm (then you can transfer them to a freezer-safe plastic bag) or proceed straight to boiling.
!On the day of:
Bring a large pot of water to boil over high heat. While water heats up, melt butter in a large skillet over medium heat. Add onion and cook until golden brown, stirring occasionally, about 10 minutes.
Once water is boiling, drop in as many pierogi as can comfortably fit (don't crowd the pot!) and boil for 8-10 minutes. They should rise to the top, then boil for a minute or so more. Remove pierogi from the boiling water, and add directly to the skillet. Let them brown for a few minutes without moving them, then remove from the pan. Repeat until all pierogi are cooked.