In a medium saucepan, melt the butter over medium heat
Once melted, add the flour and whisk continuously for about 1-2 minutes until it forms a paste (roux). This will help thicken the sauce
Gradually pour in the milk while whisking to prevent lumps. Continue to stir until the mixture thickens and starts to bubble gently
Reduce the heat to low and add the softened cream cheese. Stir until it melts completely into the sauce
Slowly add the shredded pepper jack cheese, stirring constantly until it melts and the sauce is smooth
Mix in garlic powder, onion powder, salt, and black pepper. Taste and adjust seasoning as needed
If desired, stir in diced jalapeños or bell peppers for extra flavor and texture
Pour the creamy pepper jack cheese sauce over cooked chicken breasts or use it as a dip or topping for other dishes