1. Preheat the oven to 350°F. Generously butter a baking sheet.

2. Combine the butter, brown sugar, salt, vanilla, and egg in a large bowl. Using an electric mixer or by hand, beat the ingredients to make a smooth batter. Add the flour and chocolate and stir until no traces of flour remain.

3. Drop the batter by heaping tablespoonfuls on the prepared baking sheet, spacing the cookies 2 inches apart. Bake until the edges of the cookies are barely brown, 6 to 8 minutes. Remove and let cool on a wire rack.