Preheat oven to 325°F (170°C). Spray a 10-inch enamel-coated cast-iron skillet with baking spray with flour.

In the bowl of a stand mixer fitted with the paddle attachment, beat butter and brown sugar at medium speed until fluffy, 3 to 4 minutes, stopping to scrape sides of bowl. Add egg and egg yolks, one at a time, beating well after each addition. Add peanut butter, honey, and vanilla, beating until combined.

In a large bowl, stir together flour, peanuts, baking powder, kosher salt, and baking soda. With mixer on low speed, gradually add flour mixture to butter mixture, beating just until combined.

Using a small offset spatula, spread 2½ cups (556 grams) dough into bottom and ¾ inch up sides of prepared skillet. Spread 3 cups (210 grams) Marshmallow Crème onto dough in skillet, leaving a small border around edges. Using a small spoon, dollop remaining dough all over Marshmallow Crème. Using a small offset spatula and short upward moves, drag dough into Marshmallow Crème to create a swirl as desired.

Bake until golden brown, about 40 minutes, loosely covering with foil during final 10 minutes of baking to prevent excess browning. Garnish with sea salt, if desired. Let cool on a wire rack for 15 to 20 minutes before serving. Serve with remaining Marshmallow Crème. Store in an airtight container for up to 3 days.