Melt the butter in a large skillet over medium heat and stir in the biscuits to coat with the butter. Remove from the heat and let stand for 5 minutes until the butter is absorbed. Place the biscuit pieces in a large resealable plastic bag.
Whisk together the eggs, cheese, mustard, red pepper, and milk in a large bowl. Season to taste with salt and pepper and transfer the mixture to the plastic bag. Place the bag inside another resealable plastic bag with the zipper facing another direction in order to prevent leaks. Refrigerate at least 2 hours, preferably overnight, or up to two days.
When ready to bake, preheat oven to 350 degrees. Pour mixture into a buttered 13 x 9 x 2-inch baking dish. Bake covered for 30 minutes. Uncover, add fresh herbs and bake another 30 minutes until eggs are set and the center measures 200 degrees on an instant-read thermometer.