Heat a large skillet over medium heat. Once hot, cook the bacon until it is crispy, then remove the bacon to a paper towel lined plate, and wipe out the remaining bacon grease, but don’t wash the pan.
While the bacon is cooking, bring a large pot of salted water to a boil. Once boiling, add the pasta and cook to just slightly less than al dente, according to the package instructions. Before draining, reserve 1 cup of the starchy pasta water.
In the same skillet that you cooked the bacon, melt the butter over medium heat. While the butter is melting, gently scrape up the flavorful bits on the bottom of the pan. After the butter has melted, continue to cook the butter, stirring constantly, until the butter has browned. The top will foam, and you will see golden brown specks on the bottom when it’s ready (about 4 - 5 minutes).
As soon as you see the golden brown specks, turn the heat down to medium-low and add the garlic and sage. Saute until the garlic is aromatic and the sage is crispy and has darkened (about 1 minute).
Add the kosher salt, and stir.
Mix in the cooked pasta, and 1/2 cup of the reserved cooking water. Stir to combine, and then allow the pasta to cook for another 30 seconds so that the water can absorb and combine with the sauce.
Stir in the bacon pieces, then taste and adjust the salt at this point. If you think the sauce is too thick, add a little more pasta water to thin it out.
Top with the finely grated parmesan, and serve.