Preheat oven to 200C. Stack 2 pastry sheets on top of one another, then cut in half widthwise. Line an oven tray with baking paper and place stacks 5cm apart on tray. Cut 4 x 1cm-wide strips from remaining pastry sheet and place strips over long sides of each pastry stack. Cut 4 x 1cm-wide strips widthwise and place over short sides of stacks, then trim to fit. Prick centres all over with a fork. Using a box grater, grate marzipan and scatter over the centre of each pastry stack. Bake for 15 minutes.
Meanwhile, to make cherry glaze, drain syrup from cherries through a fine sieve into a saucepan. Pat cherries dry with paper towel. Add sugar to pan and simmer over medium heat for 10 minutes or until syrupy.
Whisk extra 1 tablespoon sugar, sour cream, egg yolks and flour in a small bowl. Carefully place cherries evenly over each tart, then slowly pour cream mixture between cherries in the centre, allowing it to spread. Bake for a further 10 minutes or until set.
Scatter tarts with almonds, then drizzle with cherry glaze. Serve with double cream.