If you’ve never heard of millionaire shortbread (or gluten free millionaire shortbread, for that matter), you’re in for a real treat. The fanciest, most indulgent treatiest treat out there (maybe not but they’re not called millionaire’s for nothing). The theme of these decked out shortbread bars is: why not? Why not slather half an inch of perfectly squidgy caramel over the perfect slab of shortbread, and why not, on top of that, smear the most luxurious dark chocolate you’ll ever snap into? Why not, as a millionaire would say. So why not be a millionaire for a day and make these incredibly rich, melt-in-your-mouth squares to complement your lavish post-college…