Grease a baking dish with cooking spray and set aside.
Place the blueberries in a bowl and sprinkle with 1 tablespoon of flour. Gently stir to coat the blueberries in the flour and set aside.
Sift the flour, sugar, and baking powder into a large bowl, then whisk to mix.
Add the milk, butter, and vanilla extract and mix well. Fold in the blueberries until evenly distributed.
Pour the mixture into the prepared baking dish. Cover the dish with a paper towel and then tightly cover with aluminum foil.
Add 1½ cups of water to the removable cooking pot. Place the baking dish on a trivet or cooking rack and lower into the cooking pot.
Close and lock the lid. Pressure cook on HIGH for 23 minutes.
Once the cooking time is done, turn off the cooker and let the pressure naturally release (this will take around 10-15 minutes).
Once the pressure is released, open the lid and carefully remove the baking dish.
Remove the aluminum foil and paper towel, let the cake cool for about 10 minutes before removing from the baking dish.