In a small saucepan, whisk together the sugar and cornstarch. Whisk in water. Add blueberries and cook over medium-low heat, stirring constantly, until thickened and berries are softened, about 4-5 minutes. Remove from heat and stir in lemon juice. Set aside. (Can be made ahead and refrigerated. Simply re-warm before using to top dessert).

Preheat oven to 425°F.

Melt 2 Tbsp. in the microwave and then pour into a blender or food processor. Add the eggs, milk, flour, 1 Tbsp. sugar, vanilla extract, and salt. Blend batter until smooth. Let sit in blender, while you prepare the peaches.

Heat a 12-inch cast-iron skillet over medium heat. Add the remaining 2 Tbsp. of butter and melt. Add the remaining 2 Tbsp. sugar and cook, stirring constantly, until the sugar starts to caramelize, about 2 minutes. Add peaches to skillet and increase heat to medium-high. Cook, stirring frequently, until softened, about 2 minutes.

Briefly re-blend the batter, then pour evenly over peaches. Transfer the skillet to the pre-heated oven.

Bake pancake until puffed and golden brown all over, about 18-22 minutes. It will deflate as soon as it's removed from the oven. Don't despair. That's what it is supposed to do.

Dust pancake generously with powdered sugar and top with 3 or 4 scoops of vanilla ice cream. Top ice cream with some blueberry sauce, then serve immediately right from the skillet.