While both sugar and treacle are sweeteners, they are not interchangeable. Sugar is a kind of carbohydrate that is composed of sucrose molecules. At the same time, treacle is molasses made from cane or beet sugar. Treacle is darker in color and has a stronger flavor than sugar, so it can not be used as a 1:1 replacement. However, you can use less treacle to achieve the same level of sweetness as sugar. When baking, keep in mind that treacle will also add moisture to your recipe, so you should reduce the amount of liquid called for in the recipe. With some experimentation, you can find the right balance of treacle to suit your taste.