Sauté chopped red onion and garlic in oil until lightly caramelized.
Squeeze all liquid from spinach and lightly chop.
Place spinach, peas, potatoes, onions, garlic and cream cheese in a bowl, and mix until well combined. Salt and pepper to taste.
Put a large pot of water on to boil (add some salt to water).
In a large bowl or stand mixer, sift flour and salt together, then make a well in the center of the bowl.
Pour water and oil into the well.
If using a stand mixer, use the dough hook and knead for approximately 5 minutes (or until the dough is smooth).
If kneading by hand, incorporate the oil and water into the flour until a ball of dough forms, then turn the dough out on a lightly floured surface and knead for about 5 minutes.
Cut the dough into two parts.
Take the first half and roll the dough out on a floured surface into a long oval shape, (approximately 1/8 of an inch thick.)
Spoon half of your filling down the center of the dough that is rolled out. Take one side of the dough, lift it and lay it over the filling.
Slightly wet the dough on the other side of the filling, then lift and lay it over the filling and dough from the first side.
(The moisture from wetting the dough will help seal the dough together so that it does not open during the cooking process.)
Now, with a small rolling pin or the handle of a wooden spoon, carefully press down on the filled dough every 3-4” and on each end.
Then, with a sharp knife or scraper, cut through where the dough has been depressed with the spoon handle.
Pick up each maultasche, and seal the ends completely by pinching the dough together.
Repeat procedure with the other half of the dough and filling.
Place maultaschen on a floured sheet pan.
Gently lower Maultaschen with a slotted spoon or spider into boiling water for approximately 6-8 minutes.
Gently lift maultaschen out of water and set aside for a minute to dry a bit.
Continue on with the remaining maultaschen, being careful to not put too many in the water at once.
In a large sauce pan, sauté red onion and garlic in vegan butter until fragrant and slightly caramelized.
Deglaze pot with white wine and cook off for a couple of minutes.
Add vegetable broth and bring to a simmer for 10 minutes, then strain through a fine mesh strainer.
Return sauce to sauce pan, bring back to a simmer, and add lemon juice, salt, pepper and sugar to taste.
In a separate bowl, mix cornstarch with some water or vegetable broth and add to the pot a little at a time (until the sauce reaches the desired consistency).
Add 1/4 cup freshly chopped parsley.
In a frying pan, heat up 1/4 cup oil.
Once oil is shimmering, carefully lay maultaschen in the oil and fry each side until golden brown, (about 3 minutes each side).
Place maultaschen in a large pasta bowl, top with sautéed red onion rings and pour sauce over.
Garnish with freshly chopped parsley.