Combine the flour, sea salt, and half of the rosemary in a large mixing bowl. Incorporate the mashed potato by hand until evenly distributed throughout the flour mixture.

In a separate bowl, whisk together the warm water, yeast, and olive oil. Pour this liquid mixture into the flour bowl, stirring with a large spatula until a sticky dough forms. Briefly knead by hand for one minute until the dough holds its shape in a cohesive ball.

Drizzle or brush the top with a bit of olive oil, cover with a kitchen towel, lid, or plastic wrap, and set the bowl in a draft-free location. Let it rise until doubled in volume, approximately 2 to 3 hours.

Oil a 12-inch cast iron skillet lightly. Transfer the dough into the skillet and use your hand to gently stretch it to the edges. Press fingertips across the surface to form characteristic dimples.

Drizzle lightly with olive oil. Scatter sliced tomatoes, olives, and rosemary over the top. Optionally include other toppings like red onion, pepperoncini, scallions, or zucchini. Finish with Fleur de Sel and toasted fennel seeds. Cover and allow a second rise at room temperature for 30 to 45 minutes during oven preheating.

Preheat oven to 400°F. Bake uncovered for 30 to 35 minutes, or until the surface and edges take on a light golden hue.

Cool on a rack before removing from the skillet and slicing for serving.