Preheat your oven to 400 degrees F or 204 degrees C.
Take your puff pastry dough sheet out of the freezer to unthaw for about 15-30 minutes room temperature or 1 minute in the microwave in a towel.
In a bowl combine blueberries, sugar or sugar alternative, vanilla and lemon zest and set aside.
Put your sliced almonds in a pan and toast just until golden brown, about 5 minutes. Set aside.
Place your Puff pastry sheet on a sheet of waxed paper (parchment/baking) paper on a baking sheet. Cut your puff pastry dough into a circle using a plate or bowl. This makes enough to serve 4 people so you can decide to make 4 small tarts, 2 medium tarts or one big tart shell. Be sure to use a fork to poke a few holes in puff pastry so it does not puff up too much.
Pour the blueberry mixture over the top of the puff pastry dough be mindful to leave about a 1.5 inch around the edges. Fold and and pinch the edges of the tart to make a decorative edge. This also makes a border to keep the fruit in the tart.
Add the toasted sliced almonds on top of the blueberries. Add a dash of cinnamon, if you wish.
Bake the blueberry buckle tart for about 20-25 minutes or until the tart is golden brown.
Garnish with whipped topping, vanilla ice cream or even a little powdered sugar and enjoy!