Heat the oil in a large frying pan, add the onion and gently fry over a medium heat until the onion softens, around 8-10 minutes. Add the crushed fennel seeds, the sausage meat and a good amount of seasoning. Cook until the meat colours slightly, approximately five minutes. Stir in the gochujang and cook for a couple more minutes.
Stir in the tomato purée, vodka, balsamic vinegar and sugar, mix to combine and then add the plum tomatoes. Cover with a lid and cook, stirring occasionally until the tomatoes have collapsed.
Stir in the sour cream and cook over a low heat for around 10 minutes. Taste and season. Remove from the heat, cover and leave for around half an hour to let the flavours develop,.
To make the topping, take a frying pan and place over a medium heat. Add the butter and allow to melt, add the garlic and rosemary and fry for 1-2 minutes. Turn up the heat slightly and add the breadcrumbs and parmesan and cook for around 5 minutes until golden. Take off the heat and transfer to a bowl and allow to cool and crisp up.
When you are ready to serve, cook the pasta in well salted boiling water, according to the packet instructions, drain and reserve a little of the cooking water.
Reheat the sauce in a large pan over a low heat, add a little of the pasta cooking water to loosen if needed. Then add the pasta and stir through to coat. Serve in large bowls with a generous sprinkling of the crunchy topping.