Broccoli and Cauliflower Gratin via @PureWow. Every cook needs a few go-to vegetable side dishes in her back pocket. So let us introduce you to one that we want to serve at basically every single meal: broccoli and cauliflower gratin. It brings two veggies together in cheesy harmony, and what could be tastier than that? Confession: We love gratins. And this one is a stellar substitute for green bean or broccoli casserole.