Defrost puff pastry in the refrigerator, per package instructions.

Peel and thinly slice onion into half-moons.

Cut Brie into ¼-inch thick slices.

Heat olive oil in a medium nonstick skillet over medium heat.

Add sliced onion and cook, stirring occasionally, until onion is softened and lightly browned around the edges (about 15-20 minutes). Scrape onions into a small bowl to cool.

Lay out puff pastry sheet on a lightly floured surface.

Use a rolling pin to roll into a 12 x 12-inch square.

Cut dough in thirds horizontally and vertically, so that you have nine 4-inch squares. Place onto a parchment-paper lined sheet pan.

Swipe a bit of mustard onto each pastry, then add 1 piece of ham on each one.

Top ham with a tablespoon of the onions, and a slice of cheese.

Tuck the ham around the onions and cheese, so that you can fold over the two opposite corners of the pastry dough.

Crack egg into a small bowl, and whisk with a teaspoon of water and a pinch of salt.

Paint one exposed corner of each pastry with the egg wash using a pastry brush. Then lift up the opposite corner of the dough and press the egg washed corner on top of it to seal. Repeat for all of the pastries.

Cover the egg wash with plastic wrap and place in the refrigerator.

Move baking sheet into the freezer to chill for 30 minutes.

While pastries are chilling, preheat the oven to 400°F.

After 30 minutes, remove the pastries from the freezer and paint all of the exposed pastry dough with egg wash.

Bake for 30-35 minutes until pastry is cooked through and golden brown.

Garnish pastries with chopped chives and a drizzle of hot honey.