Speedy Kentucky Hot Browns

Ingredients

• 1/4 tsp ground black pepper
• 4 English muffins, halved
• 2 medium tomatoes, sliced
• 1 cup grated Monterey Jack cheese
• 1/4 tsp salt
• 2 cups cooked shredded chicken
• 2 tbsp unsalted butter
• 1 tsp Dijon mustard
• 2 tbsp all-purpose flour
• 1 1/2 cups whole milk