Preheat the oven to 400°F. While the oven preheats, zest the Meyer lemon into a small bowl and then slice the zested lemon as thin as possible. In a separate bowl mix the ricotta, ½ cup granulated sugar, and lemon zest.
Cut the puff pastry into 9 squares (3x3). Using a sharp knife, cut a square about ½-inch inset from the edge of each puff pastry. As the pastry bakes this will help contain the ricotta and allow the edges to puff.
Assemble the pastries by dropping 1 to 2 spoonfuls to the center of each puff pastry square. Pour ¼ cup of granulated sugar onto a plate or flat surface. Lightly dip each side into the sugar and place on top of the ricotta. Top each square with a lemon slice. Repeat with remaining puff pastry and ingredients.
Bake the puff pastry squares on a sheet pan lined with parchment paper at 400°F for 10 to 15 minutes until the pastry is golden brown. Remove the squares to platter, plate or another fire safe surface. Sprinkle each square with turbinado sugar (raw sugar) and torch until lemon is caramelized. See notes for no blow torch options.
To prepare without a blow torch, sprinkle each tart with a little more granulated sugar and broil for 2 to 3 minutes until sugar melts. The sugar will caramelize during broiling, but not as much as if done with the blow torch.)
Turbinado sugar and raw sugar are the same and are great for getting a thick caramelized layer on desserts. Regular granulated sugar can be substituted.
When cutting the inset squares, try not to cut through to the other side of the pastry dough.