Melt the butter in a pan, then add the garlic and tomtoes and let cook on a medium heat until the tomatoes begin to soften. Squash them into the pan a bit so that they begin to form a sauce (about 10 minutes or so). Then add the chorizo to the pan and let cook for a minute or two.
Meanwhile, add the passata and cream to the pan (add the cream to taste – the sauce should be a deep orangey red colour) and let bubble away for a few minutes while the pasta is cooking so that it reduces a bit. Then add most of the parmesan and stir through most of the basil.