Caramelize onions: Melt 1 tbsp butter in pan and add sliced onions. Cook until softened. Add 1 tbsp of butter when the pan starts to dry. As pan gets dry, add butter as needed. Alternatively, you can work on the onions with broth, taking care to not add so much that the pan becomes soupy.
You can make the onions a few days ahead, too! (Or make a huge batch to be used on dishes throughout the week as I do!) Once onions are finished, preheat the oven to 350.
Line a baking sheet with parchment and placed one prepared pie crust on the paper.
In a separate bowl or stand mixer with the whisk attachment, combine farmers cheese, garlic, sour cream and salt and pepper. Whisk together until well combined.
To assemble, place farmer's cheese on the pie crust, spreading evenly but leaving approximately 1 inch from the edge of the pie crust.
Top the farmers cheese mixture with caramelized onions in an even layer. Add sliced scallion, carefully pressing into the tart.
Fold the pie crust edges over to seal in the cheese and onions. If the crust cracks on the edges from folding, just press back together so the farmer's cheese does not leak out.
Brush the pie crust with the whisked egg.
Bake for 30 minutes or until edges are golden brown and the scallions crisp up.
Garnish with lemon zest and parsley if desired, allow to cool for 10 minutes, slice and enjoy!