Preheat the oven to 450°F (200°C). Grease the muffin pan, or line with paper liners.
To make the muffin batter: In a medium bowl, whisk together flour, sugar, cocoa powder, baking soda and salt. Set aside.
In another large bowl, whisk together the eggs, sour cream, orange juice, vegetable oil and orange zest.
Combine the wet and dry ingredients and mix until just combined.
Mix in chocolate chips. Don’t over-mix the batter, or your muffins will turn out tough and dense.
To bake: Divide the batter into 12 muffin cups. The muffin cups will be pretty full, and that's totally ok!
Reduce the heat to 375°F and bake the muffins for about 18 minutes, or until the inserted toothpick comes out clean.
Cool the muffins completely in the muffin pan before taking them out.