Preheat the oven to 375°F (190°C). Grease eight ramekins or oven-safe dishes with butter.
In a saucepan, melt the butter over medium heat. Add the flour and cook for about 1 minute, stirring constantly, until it forms a smooth paste.
Gradually whisk in the milk and continue cooking for another 2 minutes, or until the mixture thickens.
Remove the saucepan from heat and let it cool slightly.
Separate the egg yolks from the egg whites. Set the whites aside for later.
In a mixing bowl, whisk the egg yolks. Slowly add the cooled milk mixture, grated cheddar cheese, grated Parmesan cheese, salt, and black pepper. Stir until well combined.
In a separate bowl, beat the egg whites until stiff peaks form.
Gently fold the beaten egg whites into the yolk mixture until fully incorporated.
Divide the mixture equally among the prepared ramekins or dishes.
Place the ramekins on a baking sheet and bake for about 20-25 minutes, or until the souffles have puffed up and turned golden brown.
Serve immediately while the souffles are still hot and puffy.
Notes
Tips and Tricks
Ensure clean and dry mixing bowls when beating the egg whites. Any traces of grease or moisture can prevent the egg whites from reaching their full volume.When folding the beaten egg whites into the yolk mixture, use a gentle and sweeping motion with a spatula. This helps to maintain the airiness of the mixture.Place the ramekins on a baking sheet before baking to catch any potential spills or overflows.Avoid opening the oven door while the souffles are baking. Sudden changes in temperature can cause them to deflate.Serve the souffles immediately after baking to enjoy them at their best, as they tend to deflate as they cool.