Preheat your oven to 350F
In the bowl of a stand mixer or in a large bowl, combine the baking soda, salt, butter, sugar, and powdered sugar. Using the paddle attachment of the stand mixer, a handheld electric mixer, or a wooden spoon, combine the ingredients until light – about 3 minutes
Add the flour to the butter mixture and mix slowly until streaks of flour disappear into the dough
Gently fold the frozen berries and chopped raspberry twists into the dough using a rubber spatula. Reserve a few of each to top the cookie!
Generously butter the bottom and sizes of a 10” cast iron skillet
Using the rubber spatula, scoop the cookie dough into the skillet. Using the spatula or your hands, gently spread the dough into the skillet in an even layer.
Press the reserved raspberries and chopped raspberry twists onto the surface of the cookie dough
Bake the skillet cookie for 35-40 minutes, until the edges are golden and set and the center is still pale and soft.
Serve warm with vanilla ice cream