Beat margarine, preserves, egg, and Equal in medium bowl until smooth. Mix milk and cocoa in glass measuring cup until smooth. Mix combined flour, baking powder, baking soda, and salt into cake margarine mixture alternately with milk and cocoa, beginning and ending with dry ingredients. Pour batter into greased and floured 8-inch cake pan. Bake in preheated 350° oven until toothpick inserted in center of cake comes out clean, about 20 minutes. Cool pan on wire rack 5 minutes; remove from pan and cool completely.
Heat milk in small saucepan until very hot (do not boil). Remove pan from heat; immediately add chocolate, stirring until melted. Stir in Equal; return saucepan to low heat, stirring constantly, until smooth. Cool to room temperature; refrigerate glaze until thickened enough to spread, about 15 minutes Finishing: Place cake on serving plate, spread with Chocolate Glaze. Refrigerate until glaze has hardened, 15 to 20 minutes. Melt chocolate over low heat in small saucepan, stirring frequently; drizzle over top of cake in "lace" pattern. Refrigerate until chocolate has hardened, about 10 minutes.