1. Mix blueberries, ¼ cup sugar, flour, 1 tsp. lemon juice and elderflower syrup in medium bowl. Let sit for 30 minutes, stirring occasionally.
2. Unroll the refrigerated Puff Pastry Dough and cut out circles for 4” tart tins, making sure they are large enough to fit bottom and sides of tins. Use extra dough to cut out flower shapes (daisies, tulips) with cookie cutters (no larger than tart tins).
3. Press dough in molds firmly, placing the dough in the tins without parchment paper. Prick bottoms and sides with a fork many times. Lay piece of parchment paper over dough and add pie weights (or pie weight alternative such as dry beans) on top of parchment paper. Blind bake tarts at 375°F for 15 minutes. Remove additional paper and weights and bake for 7 more minutes until light brown.
4. At the same time, lay flower dough shapes on parchment paper and baking pan together with tarts and bake for 15 minutes until light brown.
5. While shells and flower shapes are baking, stir 1 Tbsp. lemon juice and 1 Tbsp. sugar in cup until sugar is dissolved to create lemon glaze. Brush glaze on tarts and tops of flowers as soon as they come out of oven.
6. Fill baked shells with blueberry filling and bake for 30 minutes at 375°F. When cooled, top tarts with lemon-glazed flowers.
Recipe Tip: Roll a rolling pin across the top of the tart pan to create a straight edge and remove excess dough.