Cut 3 pounds ripe tomatoes in half around the equator. Fit a fine-mesh strainer over a large bowl. Use your finger to scoop the tomato seeds into the strainer and collect the juices below (about ½ cup juice). Discard the tomato seeds. Place a box grater into the bowl and grate the cut-side of the tomato halves on the small holes of the grater. Discard the skins. You should have about 4 cups tomato pulp and juice. Finely chop 1 medium shallot (about ¼ cup) and add to the pulp.

Fit a gallon-sized freezer zip-top bag inside the insert of an Instant Pot or electric pressure cooker. Add the shallot and tomato pulp, ¼ cup fresh basil leaves, 1 cup low-sodium vegetable broth, and 1 tablespoon kosher salt to the bag. Seal the bag, pressing out as much air as possible. Freeze (with the bag still inside the insert) until solid, at least 6 hours or overnight. Remove the bag from the insert and keep frozen up to 3 months.

To cook, remove the frozen ingredients from the bag and place in the Instant Pot. Lock the lid on and make sure the pressure valve is closed. Set to cook under HIGH pressure for 5 minutes. It will take 20 to 22 minutes to come up to pressure. When the cook time is up, quick release the pressure.

Use tongs to remove the basil leaves. Whisk the soup to combine. Serve with torn fresh basil leaves, freshly ground black pepper, and a drizzle of heavy cream, if desired.