Boil your macaroni according to package instructions, draining it just before it's ready (it will continue to cook as you make the sauce in the pan, so it's worth draining a little early so it doesn't get overcooked). Return the drained macaroni to the same pan.
Add the mascarpone, and melt it through over very low heat.
Add some of the milk - just a few tablespoons initially - and mix through until you have a fairly loose sauce. You want it to be a little runny at this stage. Set the remaining milk aside.
Add the mustard and smoked paprika and mix through.
Finally, add the cheese. It's best to add it in 2-3 batches. Stir through, allowing it to melt in and create a sauce. Continue adding splashes of milk if it starts to feel too thick or dry, it often will because it's still on the heat so liquid is evaporating a little.
Once the cheese is all melted and the sauce is thick and creamy, remove from the heat and serve immediately.
