Heat olive oil in a skillet over high heat. Add the fennel and sauté until golden brown.

Once the fennel is nicely browned, lower the heat, add at least 1/3 cup water (about 80 ml), and cook for about 30 minutes. If the pan gets dry during cooking, add more water as needed.

When almost all the liquid has evaporated, deglaze the pan with at least 2 tablespoons balsamic vinegar. Let it reduce while coating the fennel.