Preheat oven to 350 degrees. Grease and lightly flour cupcake pans or line with paper liners.
In a large mixing bowl mix together sugar, flour, cocoa, baking powder, baking <g class="gr_ gr_126 gr-alert gr_gramm gr_run_anim gr_inline_cards Punctuation only-ins replaceWithoutSep" id="126" data-gr-id="126">soda</g> and salt. Add eggs, milk, oil and vanilla. Beat on medium speed of mixer for 2 minutes. Pour in boiling water and stir. <g class="gr_ gr_128 gr-alert gr_gramm gr_run_anim gr_inline_cards Grammar multiReplace" id="128" data-gr-id="128">Mixture</g> will be thin. Fill each cup about 2/3 half. Bake for 15-20 minutes or until a toothpick inserted in the center comes out clean. Cool for 10 minutes. Remove to a wire rack to cool completely.
For frosting:
In a mixing bowl beat butter and jam/jelly on medium speed until light and creamy, about 2 minutes. Slowly stir in confectioner's sugar. Mix in milk to thin out a bit for the perfect consistency.