Combine raspberries, 2/3 cup sugar, vanilla, cinnamon, lemon juice, and salt in a medium saucepan over medium heat. Stir occasionally as the mixture comes to a simmer, then reduce heat to medium-low and let it cook for 20-30 minutes, stirring frequently to prevent sticking. The filling is ready when it's noticeably thickened and jammy—you want it thick enough that it won't ooze out during baking, but still spreadable. I like to test the consistency by dropping a small spoonful onto a plate; if it holds its shape when cooled slightly, it's perfect. Remove from heat and let cool completely while you prepare the pastry—this is important because warm filling will make the pastry soggy.

While the filling cools, preheat your oven to 400°F. Remove the puff pastry sheets from the freezer and let them thaw at room temperature for about 5-10 minutes—they should be pliable but still cold. Once thawed, lay them out on a clean work surface and cut each sheet into 4 equal squares, giving you 8 turnovers total. I prefer Pepperidge Farm puff pastry because it rises beautifully and stays crispy, but any quality brand works well.

Place 2-3 tablespoons of the cooled raspberry filling from Step 1 onto the center of each pastry square. Fold each square diagonally to create a triangle, then press the edges firmly with the tines of a fork to seal them completely—this prevents the filling from leaking out during baking and creates a decorative pattern. Make sure the seals are tight; run the fork around all three edges if needed.

Arrange the sealed turnovers on a parchment-lined baking sheet, spacing them about 2 inches apart. Brush the top of each turnover with the melted and cooled butter, being generous but not excessive—this will help the sugar adhere and create a beautiful golden crust. Immediately sprinkle 1.5 tablespoons of sugar evenly over all 8 turnovers (about 3/16 teaspoon per turnover, or just a light coating).

Place the baking sheet in your preheated 400°F oven and bake for 15-20 minutes, until the pastry is puffed and deep golden brown. The turnovers should rise noticeably—this is the magic of puff pastry—and the edges should be crispy and caramelized. Start checking around 15 minutes; oven temperatures vary, so look for that beautiful golden color rather than relying solely on time.

Remove the turnovers from the oven and let them cool on the baking sheet for 5-10 minutes before serving. This resting time allows the filling to set slightly so it won't ooze out when you bite into them, while the pastry stays wonderfully crispy on the outside. Serve warm or at room temperature.