Preheat the oven to 175°C (350°F) and line a baking pan with parchment paper, leaving overhang for easy lifting.
Combine flour, butter, and brown sugar until crumbly, then press the mixture firmly into the prepared pan. Bake for 15 minutes until lightly golden.
Meanwhile, whisk pumpkin puree, granulated sugar, eggs, evaporated milk, and spices until smooth.
Pour the pumpkin mixture over the warm crust, spreading evenly. Return to the oven and bake for 40–45 minutes, or until the center is set.
Allow the bars to cool completely, then refrigerate for at least 1 hour before slicing into neat squares.