Step 1

Finely chop the onion, carrot, celery, and garlic.

Step 2

Heat the oil and butter in the pressure cooker or in a saucepan over low heat.

Step 3

Add the chopped vegetables.

Step 4

Cook 4-5 min, stirring a few times: the vegetables must soften without burning.

Step 5

Add the diced tomatoes, salt and pepper to taste.

Step 6

If you are using a pressure cooker, cover, close, and bring to high pressure.

Step 7

Cook 15 min from the time it starts to spatter.

Step 8

(Follow the manufacturer's directions to determine when high pressure has been reached).

Step 9

If you are not using a pressure cooker, simmer, covered, for about 45 min.