Preheat oven to 250 degrees F.
Add 1 pound tomatoes to a quarter-sized baking sheet with 1 tablespoon olive oil. Top with ¾ teaspoon sea salt. Shake the pan back and forth to roll tomatoes to coat.
Roast tomatoes for 2 hours, stirring a few times. Tomates can be made up to a few days in advance.
Melt 2 tablespoons butter in a 10” cast iron skillet over a medium heat.
Cut an 18-ounce tube of polenta into 1-inch medallions. Add medallions to the skillet and cover with a splatter guard. Sear polenta on each side for about 10 minutes, until crispy and dark brown around the edges.
While the polenta is searing, make the arugula pesto. Puree ½ cup arugula, ¼ cup Parmesan , and ¼ cup olive oil until thin, adding more oil if needed. Add a pinch of salt or more to taste. Careful not to over salt. Let stand and taste before adding more.
Thin out 2 tablespoons of crème fraîche with 1 teaspoon of milk.
When polenta is seared, turn off heat and add tomatoes to skillet, and remove from heat. Drizzle with creme fraiche and pesto and serve.