I think I just realised why it's so hard to get dark sugars in France
It's well-nigh impossible to find sugars like demerara, muscovado, etc. in France. In the supermarkets we have cassonade, which is a light golden sugar. Sometimes you can find organic dark brown sugar with a lovely toffee taste, great for making ginger cake, for example, but not often. But things like treacle? Forget it.
I have long puzzled over this. France had colonies in the Caribbean and part of France is in South America, so surely...
Then I heard someone talking about the unique taste of Mexican Coca Cola (really?) and the difference the sugar makes and I twigged.
I think it all goes back to the Napoleonic Wars. During the wars the British navy blockaded France and prevented trade with the colonies. This cut off the supply of sugar.
Napoleon got people doing research and development and since then France has been self-sufficient in sugar, produced from sugar beet.
This means that for two hundred years there's been no need to import sugar from anywhere else, and so those dark treacly sugars you can get from sugar cane are not widely available.