Whisk flour, eggs, milk, and salt into a smooth batter; rest 10 minutes.
Cook thin crepes in a lightly buttered nonstick pan until lightly golden.
Mix shredded chicken, cream cheese, spinach, red pepper, salt, and pepper.
Place a spoonful of filling in the center of each crepe.
Gather the edges upward and pinch firmly to form a sealed parcel.
Arrange parcels snugly in a parchment-lined baking dish.
Spoon white sauce over the parcels and top with shredded cheese.
Bake at 375°F for 20 minutes until bubbly and heated through.
Garnish with chives and serve hot.
Tip: Do not overfill the crepes so the edges can gather and seal cleanly.