Preheat the oven to 375˚F (190˚C). Place a small skillet in the oven while it's preheating (or if using a regular-sized skillet, double the recipe).
In a medium bowl, whisk together 150 g all-purpose flour, 1 tsp baking powder, ½ tsp baking soda and ¼ tsp fine sea salt.
In a separate skillet or saucepan, heat 113 g unsalted butter over medium heat until melted. Remove from the heat and add 100 g dark or light brown sugar and 100 g granulated sugar, and stir with a heat-safe spatula. It will look a little grainy and separated at this point, that's normal.
Add 1 large egg and 2 tsp vanilla extract and stir until smoothly combined. Add 170 g chocolate chips and fold in until evenly distributed.
Remove the hot skillet from the oven, and carefully add the cookie dough to it. Smooth it out, and top with some candy if you like. I recommend M&Ms, Smarties, or mini Reese's cups. Bake until the edges are puffed and the middle is just set, about 30–35 minutes.
Let the cookie cool down for 5 minutes or so, then top with some ice cream while it's still warm. Serve immediately.
