Put the thyme, bay leaf, rosemary and garlic in the middle of a piece of cheesecloth and make an herb sachet using kitchen string.
Heat a dutch oven or a heavy bottomed deep pan over medium-high heat.
Melt 1 tbsp of the butter and cook the ground lamb, making sure it is browned all over.
Add the onion and carrot, stir well and cook until they begin to get soft.
Add the beer and scrape any brown bits from the bottom of the pan.
Bring to boil and add the water.
Add the herb sachet.
Add the mushrooms and tomato sauce.
Season with salt and pepper.
Stir well and cover.
Let simmer over medium-low heat for about 1 hour, checking once in a while to stir.
In about an hour, cook pasta in pot of salted water.
When ready (7 min for al dente), strain, reserving some of the water.
Remove the herb sachet form the sauce, add the Parmesan and other 1 tbsp butter and stir. If too thick, add a little bit of the reserved pasta water and stir until nice and creamy.
Add pasta to sauce and stir well.