Preheat oven to 375 degrees.
Bring pasta to a boil and cook just under fully cooked. For example, my package instructions were for 10 minutes so I cooked only 8. You have to allow for the pasta to finish cooking while it's baking in the oven.
In the last 2 minutes of the pasta cooking time- throw the broccoli in with the pasta. Drain and set aside.
In the same pan over a low heat put the butter, garlic, and Dijon mustard in. Stir for a few seconds until the garlic becomes fragrant. Add in the flour and cook until the flour and butter mixture are well combined.
Pour a 1/2 cup of milk in and stir the sauce constantly to combine everything. The sauce will thicken quickly. Add the rest of the milk in slowly until the sauce just coats the back of the spoon. You may not need the full 2 cups so add slowly. You can keep the milk there if your sauce becomes too thick after adding the yogurt.
Remove the sauce from the heat and add in the yogurt, Parmesan Cheese, salt, pepper, and crushed red pepper (optional). Taste the sauce for the proper amount of salt and spice.
Spray a medium casserole dish (I used 8 x 10 inch) with olive oil cooking spray. Mix the pasta and broccoli with the sauce and dump into the casserole dish. Sprinkle bread crumbs and a little more Parmesan for a crisp topping. Bake at 375 degrees for 30-35 minutes or until the top is golden and bubbly.
Notes
To bump the protein in this recipe, I recommend a high protein pasta blend.