It's usually very simple to substitute brown sugar for white sugar as you can use the same amounts. The only difference when measuring the two types of sugar is that you should always pack brown sugar down firmly. For instance, brown sugar packed into a measuring cup should hold its shape at least until it comes into contact with the bottom of the mixing bowl. The main considerations to make when making this substitution are the darker color and richer taste.
Brown sugar gets its rich flavor, as well as its deep color, from molasses. The darker the brown sugar, the more molasses it contains. For example, the golden type of brown sugar has much less molasses than the darker varieties.
Many bakers prefer using brown rather than white sugar as it creates a richer tasting cake, pie or batch of cookies. Some recipes that are older may call for white sugar, as the brown variety was more difficult to get. If the result of the dessert is supposed to be flavorful, coarser in texture or have a yellower rather than white appearance, substituting brown sugar for white sugar can be a great idea.
If, on the other hand, the likely reason a recipe calls for white sugar is to help create a delicate, rather than robust, flavor as well as a light color, you may want to use honey instead. When substituting honey for white sugar, you may use half or two-thirds as much depending on how sweet you prefer your baked goods. You should also cut down some of the liquid in the recipe when substituting honey for sugar. Substituting brown sugar for white sugar can be ideal in yellow rather that white cakes. Brown sugar used instead of white in shortbread or sugar cookies may also alter the white color to give the dough a more brownish cast.
In recipes that call for both white sugar and molasses, substituting brown sugar is a good idea. You may want to cut down some of the molasses though unless you prefer an extra strong taste. Baked goods such as butter tarts may taste even better with both brown sugar and molasses added as well as a little extra vanilla. Oat, flour, white sugar and cinnamon toppings for coffee cakes, muffins or baked fruit desserts are typically improved in flavor by using brown sugar instead of white.