Preheat oven to 350°F (180°C). Place butter in a microwave safe mixing bowl. Heat in microwave until nearly melted (you want it almost all the way melted, remove from microwave just before completely melted and stir to fully melt. You just don't want it too hot or it will cook the egg and melt the chocolate chips when stirring).
To melted butter, add brown sugar, salt, 1 tbsp egg, the vanilla, flour and baking soda. Stir with a spoon until well combined, about 20 - 30 seconds. Mix in 3 tablespoons of the chocolate chips.
Shape dough into a 3 1/2-inch disk on a Silpat or parchment paper lined baking sheet, gently press remaining 1 Tbsp chocolate chips randomly over top and sides of cookie. Bake in preheated oven 12 - 14 minutes, until cookie is golden. Serve warm or allow to cool on a wire rack then store in an airtight container.
*To get 1 Tbsp egg, crack egg into a small bowl, whisk until yolk and white are well blended, then measure out 1 Tbsp. Reserve remainder for another use (aka tomorrows breakfast).
Recipe Source: Cooking Classy