Preheat oven to 350°F (175°C). Line a 12-cup muffin tin with paper liners.
In a large bowl, sift together flour, sugar, cocoa powder, baking powder, baking soda, and salt.
In a separate bowl, whisk the eggs, buttermilk, vegetable oil, and vanilla extract until combined.
Slowly add the wet ingredients into the dry ingredients, mixing gently until just combined.
Carefully stir in the hot water until the batter is smooth and thin.
Fold in the dark chocolate chips.
Divide the batter evenly among the muffin cups, filling each about two-thirds full.
Bake for 20-25 minutes, or until a toothpick inserted in the center comes out clean or with moist crumbs.
Remove cupcakes from the oven and allow them to cool completely on a wire rack before frosting.