Start by gathering all your ingredients. Make sure your spinach is completely thawed and well-drained to avoid excess moisture in your dip.
In a medium saucepan, melt the butter over medium heat. Once melted, whisk in the flour and cook for about 1-2 minutes until the mixture is bubbly and golden. This is your roux, which will help thicken the dip.
Slowly pour in the milk while continuously whisking to prevent lumps. Keep cooking and whisking until the mixture thickens and begins to bubble gently.
Reduce the heat to low, and stir in the Velveeta white queso and pepper jack cheese. Continue to stir until the cheeses have melted completely and the mixture is smooth and creamy.
Add the diced red peppers, jalapeños, and thawed spinach to the cheese mixture. Stir until everything is well combined and heated through.
You can serve this dip immediately with your favorite dippers like tortilla chips, bread, or vegetables. Alternatively, transfer the dip to a baking dish and bake at 350°F (175°C) for about 15-20 minutes until bubbly and golden on top.
