Thaw the puff pastry dough as instructed on the box (be sure to plan ahead, mine takes 40 minutes!)

Preheat the oven to 400 degrees and line 2 baking sheets with parchment paper.

Make an egg wash by beating the egg with 2 teaspoons of water.

Unfold one sheet of dough onto a cutting board and cut vertically into thirds and then again horizontally into thirds to create 9 squares of dough.

Separate the squares and roll each out a bit with a rolling pin (or you can even just stretch it with your fingertips.)

Place about 1 tablespoon of mashed potatoes in the middle of one square of dough. Fold one corner in, over the filling. Then make your way around the square, doing the same with each corner to make a pouch. Twist the ends of the dough together at the top to seal the knish. 

Repeat with the rest of the pastry squares.

With a small pastry brush (or even your fingers!), brush some egg wash across the top of each knish. Add a generous sprinkling of everything bagel seasoning (Trader Joe’s is my favorite) on top

Repeat the process with the second sheet of dough, and feel free to get creative with some mashed potato add-ins or different toppings.

Place the knishes on the baking trays, leaving a bit of space between each. (I put 9 on each tray.)

Bake for 16-20 minutes, until the tops are golden brown.

Allow to cool for a few minutes, and enjoy!