Basil Oil
Place all in skillet and bring to a boil.
Lower To a simmer for 2 mins to wilt basil. Remove heat, add pinch salt and let steep.
Let cool and food process a few times.
Sauce
Heat butter and oil, letting butter start to brown.
Add onion halves cut side down and let brown about 2 mins.
Add tomatoes and break into smaller pieces.
Add salt.
Raise heat to a boil then cover and simmer on low 20 mins.
Uncover and add basil oil.
Simmer uncovered 10 mins.
Remove and discard onions.