1. Preheat oven to 350°F and line 2 muffin pans with 15 cupcake liners.
2. In a large bowl, whisk all the dry ingredients together.
3. Add the 1 cup of milk, oil, and vanilla to the flour mixture. Stir until just combined.
4. Add vinegar, stir and scrap around the sides and bottom of bowl to incorporate all the flour. Whisk until just blended.
5. Spoon 1 full tbsp of the vanilla batter into each cupcake liner. Then add the cocoa powder and 1 tbsp of milk to the remaining batter and mix until just blended. Divide the rest of the chocolate batter into the 15 cupcake liners.
6. Using a butter knife, gently swirl the batter from the bottom up to bring some of the vanilla batter to the top.
7. Bake for about 15-18 minutes or just until a toothpick inserted in the center comes out clean. Let cupcakes completely cool before frosting.

To make buttercream:

1. Using an electric mixer, beat the butter and jam together until combined.
2. Add 1 cup of icing sugar at a time, mixing well after each addition.
3. Frost cupcakes as desired. I used a Wilton 1M tip, piping in a circular motion from the center of the cupcake outwards and back to the center. I also added some sprinkles for fun.