Preheat the oven to 400F / 200C.

Chop your onion and add it to a frying pan with 1 tablespoon of butter on low heat. Stir occasionally for about 25 minutes until golden.

Meanwhile, peel and chop your potatoes. Add them to a pot of water and bring to a boil. Simmer until potatoes are soft, about 15 minutes.

Strain the potatoes in a colander or a remove them with a slotted spoon into a medium sized mixing bowl.

To make the dough, remove 1 cup of mashed potatoes and add to another bowl. Then throw in 1 tablespoon of butter, 1 egg, 1 cup of matzah meal and a pinch of salt. Mix thoroughly the let sit.

To make the filling, add 1 tablespoon of butter to the original bowl with the potatoes. Toss in the caramelized onions, garlic and a pinch of salt and pepper. Taste and adjust salt and pepper if necessary.

To fill the knishes, lightly coat a clean work surface with cooking oil, using a paper towel to wipe or a spray can. Take an egg-sized portion of the dough and press it into a square on the oiled surface using your fingertips. Add a heaping tablespoon of filling to the center of the square. Fold up the sides and pinch well. The dough should be soft to stick together, but solid enough to fold easily. Add extra matzah meal to the dough if it’s too sticky.

Place the knishes on a non-stick baking sheet and brush with egg yolk. Bake for 25 minutes until golden. Yummy!