Preheat the oven to 350F.
Place the grated carrots on top of a double later of paper towels. Over a bowl or the sink, squeeze out the excess liquid from the carrots, set drained carrots aside.
In a large bowl, add the melted and cooled butter as well as the granulated sugar and the brown sugar. Mix with a nonstick spatula to combine, mixture will still look slightly separated. Add in the egg and mix until mixture thickens. Add in the grated carrots and mix until combined. Add in the the flour, baking soda, cornstarch, kosher salt, chopped white chocolate and chopped walnuts all at once. Mix to form a thick dough.
Press the dough into a small skillet (I used a 6 inch but you can use an 8 inch skillet as well ), pressing it to just below the top of the pan to leave room for it to puff as it bakes. The smaller the skillet, the more dough you will have leftover. Extra dough can be refrigerated for up to 2 weeks or frozen for up to 3 months.
Bake for 13-15 minutes, until top is golden borwn and edges are puffed. For a gooey center cook on the shorter side closer to 13 minutes.
