Preheat the oven to 425℉/220℃/Gas Mark 7.
In a large bowl, whisk the all-purpose flour, granulated sugar, cocoa powder, baking soda, baking powder, and salt together. Set aside.
In a medium bowl, beat the eggs, sour cream, vegetable oil, milk, and vanilla extract until mixed well.
Pour the wet ingredients into the dry ingredients and mix with a silicone spatula. Take care not to overmix.
When the ingredients are fully incorporated together, add the chocolate chips and mix again.
Take your muffin in and spray with non-stick spray or use muffin liners and fill each space level. Add the sea salt here for garnish if desired.
Bake at 425℉/220℃/Gas Mark 7 for 5 minutes, and with the muffins in the oven, reduce the heat to 350℉/176℃/Gas Mark 4.
Continue to bake for 20 minutes. If making mini muffins, only continue to bake for another 15 minutes. To test if they are done, insert a toothpick and if it comes out with just a few moist crumbs or clean the muffins are done baking.
Remove from the oven and let cool in the muffin tray then remove and continue to let cool on a cooling rack.