Chop the chocolate into small chunks and set aside.
Beat the butter until creamy, then add the salt and vanilla. Scrape sides of bowl and add the sugar. Scrape side of bowl again and add the egg, then beat until blended.
By hand, gradually stir in the flour until blended. Stir in the chocolate chunks.
Using a rounded teaspoon, scoop about 40 (or slightly more) drops of dough onto foil lined plates or a foil lined baking sheet. Chill the dough thoroughly, then when it is cold and firm, shape the mounds of dough into neat balls.
Preheat the oven to 400 degrees F (for the smaller cookies). Line a baking sheet with parchment paper (do not attempt to grease it as this makes the surface too slippery and the cookies will spread and burn). If you don’t have parchment, you can use a Silpat or plain foil.
Arrange dough balls 2 ½ inches apart on a baking sheet and bake for around 7 minutes or until edges are brown and centers appear set. Remove from oven and let sit on the baking sheet until the cookies can safely be transferred to a wire rack. Let cool completely.