Heat together butter and brown sugar in a sauce pan until sugar melts completely, then remove pan from heat and cool it to room temperature.
Add egg and vanilla and mix well using egg beater.
Sift together dry ingredients including flour, cocoa, baking soda and salt.
Gradually fold this mixture with the egg mixture, it would become sticky dough, cover it and set aside for 30 min until it sets so that it can handle easily.
After that roll the dough to ¼ inch thick on a flat surface and then cut using heart shape cookie cutter.
Place them on a dusted and greased baking tray keeping 1 inch distance between each cookie. Bake for 10 min at 350 degrees F.
Mean while prepare topping for the cookies, for that cook chocolate, butter and sugar together on medium heat until all the chocolate melts completely.
When the cookies become ready cool them to room temperature and then dip in the prepared chocolate sauce. Leave for few minutes at room temperature until topping would set.