Heat olive oil and butter in a pan and add the onion.

Cook over medium-low heat until onion is just starting to turn brown.

Add the celery and carrot and cover and cook, stirring occasionally until just starting to brown.

Stir in the garlic and cook for 1 minute.

Turn up the heat to medium and add ground beef and brown.

Stir in the tomato paste and cook an additional minute.

Turn the heat to low and cover and cook for 1 ½ hours.

(Add water ½ cup at a time if the sauce seems to be drying out. Meat should be covered with sauce.)

Serve over tagliatelle.