How to Make It
Preheat oven to 400°F. Using a hand mixer or a wooden spoon, beat together spinach, cream cheese, garlic, shallot, and butter until smooth, about 2 minutes.
Add mozzarella, parmesan, mayonnaise, salt, pepper, and paprika. Mix until combined. Gently stir in chopped bell pepper. Set mixture aside.
Take one sheet of puff pastry and place on parchment paper lined baking sheet. Take spinach mixture and spread onto surface of puff pastry in shape of a Christmas tree (a tall triangle with a small square at the base). Leave a 1/4-inch border on the edges of the pastry without any spinach mixture spread onto it.
Take second puff pastry sheet and place it directly on top of the first pastry sheet. Using your hands, feel around the spinach mixture underneath the pastry and press around the edges, sealing the two sheets of pastry together around the spinach mixture. Using a paring knife, cut 1/4 inch around the outside of the spinach mixture. Remove the excess pastry. The pastry left should be in the shape of a Christmas tree.
Starting on the right side of the widest part of the Christmas tree, cut a straight line from the edge of the tree to 1-inch from the center. Repeat cuts like this up the tree every 1/2 inch, ending each cut a little closer to the center of the tree as you get closer to the top of the tree. (This creates the look of a tree trunk getting smaller as it goes up the tree.) Leave the very top of the tree as a small uncut triangle.
Repeat cuts on the left side parallel to the cuts on the right side of the tree.
Carefully lift each pastry strip from the end and turn the end of the pastry strip away from yourself to twist the “branch,” accomplishing 3 full twists for each strip. (The strips at the top of the tree may only allow for two twists.)
When all of the pastry strips have been twisted, brush the entire surface of the pastry with the beaten egg. Sprinkle the surface with a few pinches of kosher salt.
Bake for 25 minutes, rotating the baking sheet halfway through baking. Allow to cool completely before serving.