Preheat oven to 350°F. Grease your pan with butter, making sure to get the sides well greased as well as the bottom.
Add milk, 1/3 cup sugar, eggs, vanilla, salt, and flour to a blender, and blend at top speed until fully mixed and aerated, about 1 minute.
Pour enough batter into the pan until it's about 1/4 inch deep. Put the pan on the stove on low heat for 2-3 minutes, to let the bottom start to cook and set (like we're slowly making a pancake). Remove from heat.
Spread the blueberries evenly over the batter and then sprinkle them with the leftover 1/3 cup sugar. Pour the rest of the batter over the berries and gently mix with a spoon if some of the berries and sugar didn't get coated with batter. Place into the oven on the middle rack and bake for about 50 minutes. The top will be puffy and brown.
Remove from the oven, and slice into pieces to serve. If you're making this ahead of time, make sure it's still being served warm! Wait until serving to dust with powdered sugar, or else it will melt into the top.
Enjoy!
