Preheat the oven to 400° F / 205° C. Line a half-sheet rimmed baking tray with parchment or a silicone baking mat.

On a silicone rolling mat or lightly floured work surface, unroll puff pastry and trim to approximately 10 x 14 inches. (If your pastry sheet is a square instead of a rectangle, use a rolling pin to roll it a few inches longer.)

With a pastry brush, lightly egg wash the entire surface of the pastry. Scatter generously with everything bagel seasoning.

Flip onto prepared tray, seasoning side down. Prick the top with a fork or docking tool. With a pastry brush, apply a strip of egg wash around the outside edge.

Fold edges over, creating a 1/2-inch border. Brush with additional egg wash. Sprinkle folded edge with more everything bagel seasoning.

Bake in preheated oven for 25-30 minutes, or until flaky and golden brown. Set aside to cool while you prepare the cream cheese layer.

In a medium bowl, combine cream cheese, mayonnaise, and lemon juice. With a hand mixer, mix on high speed until smooth and creamy, about 1 minute. Mix in the chopped dill. Season with salt and pepper to taste.

With a small stepped palette knife, spread cream cheese mixture over cooled pastry, allowing a 1/2-inch border around outer edge.

Top with smoked salmon, capers, and red onion. Season with salt and pepper. Garnish with chopped dill.  

Slice into squares and serve.

This puff pastry smoked salmon tart tastes best on the day it is made. Wrap leftovers in foil and store in the refrigerator for up to 1 day. Eat cold.