Preheat an oven to 350 F.
In a 10 inch cast iron skillet, melt the butter over medium-low heat. Cook, swirling occasionally, until the butter is golden brown and nutty smelling (see blog post for instructions on how to brown butter). Pour the butter into a heat-proof mixing bowl and let it cool slightly.
While the butter cools, toss the blueberries, white sugar, lemon zest, juice, and corn starch together in a separate mixing bowl until the blueberries are well coated.
Whisk the sour cream (or skyr), vanilla extract, and buttermilk into the cooled brown butter until smooth, then whisk in the brown sugar. Fold in the flour, baking powder, and sea salt until the batter is smooth and no lumps of flour remain.
Pour the batter into the skillet you used to brown the butter and then top with the blueberries in an even layer. Bake for 35-40 minutes until the edges are golden brown and the middle is cooked through.
Cool for 15 minutes before serving warm. Top with a dusting of powdered sugar and whipped cream or ice cream.