Preheat the oven to 375 degrees.
Heat the oil and butter in a large dutch oven over medium heat until shimmering, but not smoking.
add the onion and cook stirring occasionally for about 2min.
Add the garlic and cook until fragrant, about 2 min.
Increase the heat to med-high and add the meat, salt and pepper; cook, breaking the meat into small pieces with a wooden spoon.
cook until the meat has lost its raw color, but has not browned, about 4 min.
Add the cream and simmer, stirring occasionally until the liquid evaporates and only the fat remains, about 4 min.
Add the herbs, pureed, diced tomatoes, and tomato paste, and bring to a simmer; reduce to low and simmer slowly until the flavors blend, about 3 min.
set aside. (the sauce can be cooled and stored for 2 days and then reheated and assembled.)