If you're aching to making some delicious cobbler or cookies that call for a cup of brown sugar and find your pantry wanting for that key ingredient, never fear. While nothing matches precisely in taste or chemistry, you can whip up a dish or goody with a fairly comparable taste, texture and weight.
White Sugar and Molasses
Brown sugar contains sugar and molasses. The closest you can get to this without having the real thing is to mix some white granulated sugar with molasses. Blackstrap molasses work well for substituting dark brown sugar. Otherwise regular molasses does just fine. Add just a couple of tablespoons of molasses at a time. You don't want to add too much weight to your recipe, and white sugar already weighs a bit more than brown sugar -- even packed brown sugar. If you don't have the molasses, substitute it with white granulated sugar (1 cup of white sugar for 1 cup of packed brown). Do know that it won't taste exactly the same as with brown sugar.
If you're in a pinch, honey can add weight and sweetness to your recipe in a similar way that brown sugar does. It's important to remember that honey weighs more than brown sugar. A cup of honey weighs 340gr, while a cup of packed brown sugar weighs only 227gr or so. Honey is also sweeter than sugar and adds acidity to your ingredients. You can neutralise this with just a pinch of baking soda. Honey also causes baked goods to cook quicker. Because of this and the fact that honey doesn't attract moisture, baked foods can dry out quicker. You can adjust the weight and sweetness simply by adding less, but do know that your dish won't taste exactly the same as it would with packed brown sugar.
Let's say you want to skip the granulated sugar or are out of it. You also have no molasses. You can substitute maple syrup for sugar as a sweetener, but it must be 100 per cent maple syrup. You should only use 3/4 cup maple syrup for each cup of packed brown sugar the recipe calls for. Also, for each cup of syrup that's used in the substitute recipe, 3 tbsp of liquid should be removed from the recipe. So, if you use 2 cups of syrup baking a cake, you would reduce the water, milk or whatever liquid it calls for by 6 tbsp.