In a large skillet, melt the butter over medium heat. Add the 3 cups of diced loaf bread. Spray the bread cubes with olive oil, then sprinkle the garlic powder and Kosher salt over them. Let them brown for 3-4 minutes, stirring occasionally.
Spray bread cubes with olive oil as needed if bread cubes look dry.
Continue cooking over medium heat until golden brown and crispy, approximately 8 minutes.
Remove from the skillet and let it cool to room temperature.
Use immediately or store in a jar in the refrigerator for a week.