Drain cherries, reserving juice. Halve any large cherries. In a medium mixing bowl beat butter with an electric mixer in medium to high speed for 30 seconds. Add the sugar, baking powder, baking soda, and 1/4 teaspoon of salt. Beat until combined, scraping sides of bowl. Beat in egg and vanilla until combined. Beat in cocoa powder and as much of the flour as you can with mixer. Stir in remaining flour using a wooden spoon. Shape dough into 1-inch balls. Place balls about 2 inches apart on an ungreased cookie sheet. Press your thumb into the center of each ball. Place a cherry in each center. For frosting, in a small saucepan combine chocolate pieces and sweetened condensed milk. Cook and stir over low heat until chocolate is melted. Stir in 4 teaspoons reserved cherry juice. Spoon 1 teaspoon frosting over each cherry, spreading to cover (frosting may be thinned with additional cherry juice if necessary). Bake in a 350 degrees oven for 10 minutes or until edges are firm. Cool 1 minute on cookie sheet. Transfer to a wire rack and let cool. Note: Do not substitute imitation chocolate pieces.