Preheat the oven to 350°F and line a 12 cup muffin pan with paper liners.
Whisk together the flour, cocoa powder, baking soda, and salt in a medium bowl. Set aside.
Melt the chopped baking chocolate in a microwave-safe bowl in 20-second intervals, stirring between each, until smooth
.Let it cool slightly but keep it warm.
In a large bowl, whisk together the melted chocolate and vegetable oil until fully combined.
Add the granulated sugar and brown sugar and whisk vigorously for 1–2 minutes until glossy and slightly thickened.
Add the eggs one at a time, whisking very well after each addition.
Continue whisking for another 1–2 minutes until the mixture looks shiny and slightly lighter in color.
Whisk in the milk until smooth and fully incorporated.
Add the flour mixture to the bowl and gently fold with a rubber spatula just until no streaks of flour remain. Do not overmix.
Fold in the chocolate chunks until evenly distributed.
Divide the batter evenly between the muffin liners, filling each about ¾ full.
Bake for 18–22 minutes, or until the tops are shiny and cracked and a toothpick inserted in the center comes out with moist crumbs. Do not over bake.
Let the muffins cool in the pan for 5–10 minutes before transferring them to a wire rack to cool completely.