Preheat oven to 400. Place the garlic head in a small piece of aluminum foil, drizzle with oil, seal and roast for 35 minutes. Remove from heat and set aside.
In a small sauce pot, melt the butter. Add the flour, whisking constantly for 1 minute. Slowly add the milk, continuing to whisk another 5 minutes or so until the sauce gets thick and creamy. Add in the herbs, a generous pinch of salt and pepper and whisk a little more. Transfer cream sauce to a small food processor or blender. Add the roasted garlic cloves by squeezing them out of the skins and pulse sauce until very smooth. Cover to keep warm.
In the meantime, heat a medium skillet over medium high. Add the sausage and break up with a wooden spoon, cooking until browned all over, 6-8 minutes.
Also in the meantime, bring a large pot of salted water to a boil. Add the pasta and boil until al dente. Drain and return to the pot.
Pour the cream sauce over the pasta, along with the spinach and sausage. Toss to coat until spinach just begins to wilt. Taste for seasoning. Serve hot.