Boil your pasta in well salted water. Reserve a cup of pasta water before draining, you might not need it but it's good practice!
In a small bowl or ramekin, mix the miso and hot water together. This helps to loosen the miso paste and makes it easier to mix in to the cream. Set aside.
In a large skillet that will fit all the pasta in at the end, melt the butter over a medium heat and add the garlic.
Let it gently sizzle for a minute, careful not to let it brown.
Add the cream and black pepper and bring to a VERY gentle simmer. Lower the heat slightly so it is barely bubbling and add the grated parmesan in 2 - 3 lots, letting it melt into the cream before adding more.
Add the miso mixture and mix in well, a whisk is helpful here.
Add the lemon juice and whisk in quickly. Let it gently thicken for 1 - 2 mins at a very gently simmer (not too many bubbles!).
Add your cooked pasta in, toss and let it gently bubble for a min or two. Add some pasta water if you need to loosen.
Cream sauces thicken up really quickly off the heat so make sure it is quite 'saucy' in the pan.
Serve with the fresh rosemary on top.
Watch the quick video below to see it come together!