1) Defrost spinach in microwave. Wring out and separate, reserve.
2) While the spinach defrosts, bring a large pot of water to a boil over medium heat for the pasta and a pan with a few inches of water to a boil over medium heat for the long stemmed broccoli. Salt the boiling water and cook pasta to just-shy of al dente. Cook the broccoli for 3 minutes, then refresh in a bowl of cold water and drain well.
3) Return the pan that you cooked the broccoli in to the stove top over medium heat and add 45g butter. When the butter has melted, whisk in the plain flour and cook for 1 minute. add the milk and whisk to combine. Cook the sauce for 5 minutes, to thicken, then season with salt, pepper and nutmeg, to taste. Reduce the heat to low. when pasta is almost ready, and the provolone and asiago cheeses to the sauce.
4) Heat the grill or the oven to high.
5) In a large bowl, combine the pasta with the spinach, broccoli and sauce. Transfer to individual ramekins or a large single baking dish. Top with the Parmesan cheese and brown under the grill or in hot oven for a couple of minutes. Remove from the oven and serve.