Boil your pasta in well salted boiling water for 2 minutes less than package instructions. Reserve a cup of pasta water before draining. I boil my pasta when the tomatoes get added to sauce but feel free to do it first. Doesn't matter if it's cold when added to sauce.
Pre heat your broiler or oven grill.
In a large fry pan over a medium heat, gently fry the onion in the 1 tbsp olive oil and 1 tbsp butter for 5 - 6 minutes until soft and glassy. Turn heat down if browning.
Add the garlic and cook for a further 1 - 2 minutes. If you would like a little spice then add ½ tsp of chilli flakes too.
Add the tomato paste and continue cooking and stirring for a good 5 minutes. It helps to enhance the flavor.
Add the tomatoes, vodka and ½ cup of water (I slosh the ½ cup of water in the tomato tin!) and mix well. Cook at a VERY gentle simmer for 10 minutes. This is often when I will cook the pasta if I don't do it before.
If you would like the sauce to be smoother feel free to puree it at this stage.
Add the cream, lemon juice, salt and black pepper and whisk in well. Your heat should be low here, it should never be boiling.
Add 70 grams of the finely grated parmesan cheese in two or three separate lots, letting each addition melt before adding in more.
Stir through the remaining 4 tbsp (50g) of butter.
Add your cooked pasta, ½ cup of the pasta water and mix through well. Taste for seasoning.
Feel free to eat it now as is if you would prefer not to crisp up the top.
Pour into your baking dish (I used a 32cm round dish) and sprinkle with the remaining 120 grams of parmesan.
Broil (or grill) for 5 minutes. Keep a close eye on it! You want the top to be golden brown with a few charrred bits happening too!