In a large bowl, beat the butter until fluffy. Add the brown sugar and granulated sugar and beat until well blended. Add the egg and vanilla and beat until thickened. Beat in the melted chocolate, then add 0.75 cup of the flour along with the baking soda and salt. Stir in the remaining 1 cup flour to make a soft dough.
Divide dough in half. Wrap each half in plastic wrap and shape it into a 15 cm log. Refrigerate until firm. (Can be stored in a plastic bag and refrigerated for up to 1 week or frozen for up to 2 months.) Preheat oven to 350. Using a thin knife, slice each log 0 cm to 1 cm thick. Arrange the cookies 3 cm apart on a buttered cookie sheet and bake for 10 to 15 minutes or until lightly browned.
VARIATIONS: Chocolate Mint: Add 1 teaspoon of peppermint extract to the dough with the vanilla.
Double Chocolate: Add 2 ounces of chopped semisweet chocolate.
Chocolate Macadamia: Add two third cup of finely chopped unsalted macadamia nuts. Roll each log in one third cup of finely chopped macadamias.
Chocolate Hazelnut. Add 1 cup of finely chopped, toasted and peeled hazelnuts. If desired, roll each log in one third cup of finely chopped hazelnuts.
Chocolate Peanut: Add 1 cup of finely chopped unsalted roasted peanuts. If desired, roll each log in one third cup of finely chopped peanuts.