Cook your pasta in a pot of well salted boiling water until al dente, in a creamy sauce you don't want it in there too long so undercook it by a minute. Reserve some pasta water before draining.
When cooking time is getting close start your sauce.
Squeeze as much water out of the frozen spinach and set aside.
Heat the butter over a medium heat in a large frypan and when foamy and melted add the fresh herbs and garlic, cooking gently for 1 - 2 minutes (try and time this so you can get the cream in before anything is catching or browning in the pan)
Add the cream and whisk well gently scraping anything off the bottom.
Lower the heat slightly if needed and add the lemon juice, letting it seperate and then come back to an emulsion by whisking for 30 seconds or so.
Add the parmesan in a few additions, whisking until it has just melted and incorporated.
Add your cooked pasta straight in and mix.
Add ¼ cup of pasta water and let it all gently bubble away for a few minutes, just at a slightest of simmers, never boiling.
This sauce will never thicken much so you want to see it bubble to know it is doing something.
When most of the pasta water has cooked off add another ¼ cup, add the spinach and sausages and cook for another couple of minutes.
If you've undercooked your pasta right it should be a perfect consistency by the time it has been bubbling away in the sauce for 4 - 5 minutes.
Season with a few big cracks of black pepper to taste and lots of parmesan on top!