Heat oven to 350°.

Melt butter in a 10- to 12-inch cast-iron skillet. Remove the pan from the heat and whisk in sugar and brown sugar. Set pan aside to cool slightly.

In a bowl, whisk together flour, baking soda and salt; set aside. Crack egg into a bowl and whisk with vanilla extract. Whisk egg mixture into the skillet and fold in flour mixture with a spatula until just combined. Stir in chocolate chips and oatmeal. Even out batter with a spatula.

Bake until edges are brown and top is golden, 35 to 40 minutes. Transfer to a wire rack to cool, 15 to 20 minutes. Serve warm or at room temperature topped with a scoop of ice cream.

TIPS AND TRICKS FOR CARING FOR CAST-IRON COOKWARE

To clean your pan initially, dump in ½ cup kosher salt and scour it with a wet cloth—this will help remove the factory coating. Wash well with soap and water and dry completely. NEVER put your pan in the dishwasher!

Seasoning a cast-iron pan is essential, for it creates a valuable nonstick cooking surface. To season your cast-iron cookware, follow these three simple steps: Wipe a thin layer of vegetable oil on all the pan surfaces, including the sides, handle, lid and so on. Place in a 400° oven for 1 hour; then let cool in the oven. Repeat this three or four times, until your pan appears to have a good sheen on the surface. Don’t scrub the good seasoning away with soap, unless the pan is super dirty. To clean your cast-iron cookware, simply scrape off any stuck-on food, rinse and dry.

To prevent rust from forming, dry pans thoroughly before putting them away. I heat mine over a moderate gas burner until it is dry—you could also put them in a hot oven for a few minutes. While the pan is still warm, rub on a very light coating of vegetable oil with a paper towel or cloth.