I have a recipe for oatmeal cookies that uses demerara sugar. While I do have some demerara sugar, the quantity remaining is approximately 1/3 of what is needed for the recipe. (In normal circumstances I'd just go buy more but...)
What I do have is plenty of several other sugars: white caster sugar, golden caster sugar, light muscovado and dark muscovado. (The best substitutes suggested by google are granulated brown sugars which unfortunately I don't have.)
Is there any one or combination of these that could be used to make up the remaining 2/3 weight of sugar while limiting the effect on the end result? (The recipe has the sugar creamed into butter, if this makes a difference.)