Preheat your oven to 180°C.
Spread the puff pastry roll on a large baking sheet. Trim the edges to form a rectangle (if desired). You can also keep the circular shape.
Peel and cut the pears lengthwise into thin slices. Arrange them on the puff pastry.
Place a few knobs of butter on top.
Sprinkle the vanilla sugar over the entire surface of the tart.
Bake for about 30 minutes until the tart is golden brown.
Leave to cool on a rack and spread the pieces of speculoos on top.