Sugar – Brown sugar instead of white sugar

Normal cassonade is cane or candy sugar with added molasses (I don't know what the exact difference is with brown sugar, I think cassonade is just a type of brown sugar.), however this cassonade is from sugar beets.

My best guess to replicate it is to put some regular granulated sugar for a couple of seconds in a blender, so the size of the particles is smaller. Then add some molasses and if you can find it, a drop of inverted sugar syrup. I've also found that there is caramel added in Cassonade Graeffe, but I don't know whether they add that flavour or they caramelize the sugar for a short amount of time. If I find the time, I will try to find out more, but it's not a product with a lot of information about.

If you just want a close alternative, I would advise you to just buy different kinds of brands of brown sugar. Perhaps, one will be softer than the other (I don't live in the US, I can't speak to that). Try to find brown sugar from beets, not from cane sugar (not sure if this is available). Or if you're willing to pay the taxes and shipping costs, I can send you a package.

The in the US, light brown sugar always means the one in the bottom left. The bottom right is dark brown sugar and has a higher molasses content. In the US, I typically see the 'brown sugar' in the upper right referred to as 'raw sugar' or the brand 'sugar in the raw'. If you're using a US recipe, it needs the bottom left.

If you don't have any and its an ingredient like in brownies, try adding the molasses and sugar as separate ingredients. 1 Cup of sugar + 1 tablespoon of molasses is about the right ratio for light brown sugar.

If you can't get molasses...try dark corn syrup, honey, or depending on the flavor your want, maple syrup. (A comment from @JasonTrue above mentions that beet syrup is an option as well, althought I haven't tried it.)