In a medium stock pot, warm the beans up over a low heat.
Add the tomato paste and a splash of water. Stir gently until combined, careful not to break up the beans. You don't need to cook it at this stage. I just warm it up so that the tomato paste can break down.
Add the turnip tops, ricotta cheese, Italian herbs, and red pepper flakes, and stir to combine.
Transfer the mixture to a casserole dish. I used a square dish about 8"x8"
Sprinkle the top with Fontina cheese and oregano.
Bake in the oven uncovered for 10-15 minutes until the cheese melts. I put the broiler on for just a few seconds to make the top brown and bubbly.
I served this casserole with crusty Italian bread drizzled with extra virgin olive oil
You can substitute cannellini beans for the butter beans.