In a large bowl, whisk together the flour, kosher salt, instant yeast, and sugar until well blended.

Gradually pour in the cold water, gently mixing it in until a shaggy dough forms.

Add the large egg, warm milk, and melted butter to the dough. Stir until the mixture is smooth and well combined.

Cover the bowl tightly with plastic wrap and set it aside at room temperature for around 2 hours.

Preheat your oven to 375°F (190°C).

Once the dough has risen, shape it into rolls of your desired size and place onto a baking sheet lined with parchment paper.

Using a pastry brush, gently apply the beaten egg mixture on top of each roll.

Bake for about 20 minutes, or until they are golden brown and puffed up.