Break up the brown sugar by pressing it through a small fine-mesh sieve or rubbing it between your fingertips so there are no clumps.
Add the brown sugar, cinnamon, cloves, cardamom, ginger, nutmeg, and allspice to a small bowl.
Whisk until the blend is completely uniform in color.
Transfer to a small airtight jar, label with the date, and store in a cool, dark place.
Notes
Why a small batch: I make this blend in a small batch on purpose. Ground spices start losing their aromatic oils as soon as they're exposed to air, light, and heat, so a blend is at its most flavorful in the first few weeks after you mix it. A small batch gets used up while it's at its best, and when you run out, a fresh batch takes just five minutes. Want more for holiday baking? Double or triple the recipe, but plan to use it within a few months. Freshness matters: Check the dates on your ground spices before you start. If a spice doesn't smell strong when you open the jar, your blend won't taste strong either. Storage: Keep it in an airtight glass jar in a cool, dark cupboard for the best flavor within 3 to 6 months. Shake before each use, since the brown sugar can settle or clump. Sugar-free option: Leave out the brown sugar for a pure spice blend that works in both sweet and savory recipes.