Begin by filling a large pot with water and adding a generous pinch of salt. Bring to a rolling boil over high heat, about 5–7 minutes. Peel and chop yuca into 2-inch chunks.

Once boiling, add the chopped yuca pieces. Reduce heat to medium-high and simmer for around 30 minutes until fork-tender.

Drain the yuca in a colander, reserving about 1/4 cup of the starchy cooking water.

Cut each yuca piece in half lengthwise to remove the fibrous center, then place into a mixing bowl.

Add the reserved cooking water and butter (or olive oil) to the bowl. Mash thoroughly until smooth and creamy.

Taste and season with salt. Serve hot, topped with sautéed red onions.