In a large bowl, combine blueberries, sugar, cornstarch and lemon juice and zest together until fully combined.
Spread puff pastry out on a parchment lined baking sheet.
Place blueberry mixture in centre of puff pastry, leaving 2-3 inches of space between the blueberries and the edges.
Gently fold the edges on the pastry in toward the centre, overlapping the sides to form an oval or circle. Press the edges together to seal.
Brush the outside of the pastry with the beaten egg and sprinkle sugar over the egg wash.
Place the galette in the fridge while preheating, at least 15 minutes.
Preheat oven or smoker to 400℉.
Bake for 30 to 35 minutes or until the pastry is golden.
Allow to cool on the pan to room temperature before slicing and serving.