Step 1

Add the olive oil to a large saucepan over medium high heat.

Step 2

Saute the onion in the olive oil until soft.

Step 3

To the sautéed onions, add the San Marzano and the diced tomatoes together with all their juices.

Step 4

Add salt and pepper.

Step 5

Cook at a high simmer for about ten minutes.

Step 6

Puree the soup by transferring to a blender in small batches or use an immersion blender directly in the pan. (If using a regular blender, return the pureed soup to the pan.)

Step 7

Reduce the heat to low and whisk in the sour cream and tarragon.

Step 8

Garnish each with a dollop of sour cream and a little tarragon if desired.