Molasses is a bit of a weird ingredient! It's a super dark, sticky byproduct of sugar production. As I mentioned earlier in the post, molasses can be substituted for black treacle if you're in the UK. They're very similar in taste and texture. If you can't get your hands on treacle or molasses, you can simply substitute it for another tablespoon of agave or maple syrup. If you do this, I'd also recommend substituting the caster sugar for brown sugar. This way, you'll still get a nice chewy texture from the little bit of molasses that the brown sugar contains.