Slice the brioche buns into 1-inch-thick by 1-inch big cubes. Keep the buns whole, do not slice in half. If they come pre-sliced, keep the bun whole while slicing into cubes.
Select the Preheat function on the Cosori Smart Air Fryer, adjust the temperature to 355°F, time to 5 minutes, then press Start/Pause.
Add the bread cubes into the preheated air fryer basket. It’s okay if some overlap or are stacked upon each other.
Set the temperature to 355°F, time to 5 minutes, then press Start/Pause.
Transfer the bread cubes from the fryer basket onto a large cutting board or plate. Allow the bread to cool completely.
Combine the water and sugar into the saucepan and bring to a simmer, about 5 minutes, then add in the butter and milk. Once the butter is completely melted, lower the heat and stir until a bubbly, foamy caramel has formed. Remove the pan from the stove and set on a heat resistant surface.
Toss the cooled bread cubes into the pan and evenly coat the bread cubes on all sides.
Transfer the coated bread cubes onto a parchment paper lined flat surface and separate each cube so they don’t stick together. Allow it to cool for 5 minutes.
Serve the popcorn bread in popcorn bags and enjoy!