Prepare the pan: Line the springform tin with parchment paper and set aside. Heat the oven to 320°F (160 °C).
Mix dry ingredients: In a large bowl, whisk together the flour, cinnamon, and sugar.2 ½ cups all-purpose flour + 1 teaspoon cinnamon + ½ cup granulated sugar
Add the butter: Cut the cold butter into small cubes and add it to the bowl. Rub it into the flour mixture with your fingertips (or pulse everything in a food processor) until the dough begins to clump together.1 cup unsalted butter
Chill the dough: Bring the dough together with your hands and press it evenly into a rectangle. Wrap it in plastic wrap and chill it for 30 to 60 minutes (or until the next day) (Note 2).
Roll or press the dough evenly into the prepared pan. Use a fork to prick the dough all over (optional).
Bake cinnamon shortbread: Place the tin in the oven and bake for about 35–45 minutes, or until the surface looks set and lightly golden around the edges.
Cut while hot: Remove the shortbread from the oven and, while it’s still hot and soft, cut it into triangles directly in the tin.
Cinnamon mixture: Mix cinnamon and sugar in a small bowl. Sprinkle the shortbread generously with cinnamon sugar right after cutting, so it adheres well.2 tablespoons granulated sugar + 1 teaspoon cinnamon
Cool fully: Let the shortbread cool completely in the tin before lifting it out (Note 3).
Notes
Measurements: I always recommend using a digital kitchen scale in baking; it guarantees the best results.
Shape: You can roll the dough into a rectangle or square about 2 cm (¾ inch) thick, bake on a parchment-lined tray, and cut into pieces while still warm for neat, even shortbread.
Storage: Store in an airtight container at room temperature for up to a week, or freeze for up to 3 months.