Preheat your oven to 180°C (350°F). Line a jumbo muffin tin with paper liners.
In a large mixing bowl, whisk together the eggs, brown sugar, milk, sour cream, vegetable oil, and vanilla extract until well combined.
Sift together the flour, cocoa powder, salt, baking powder, baking soda, and optional espresso powder.
Gradually fold the dry ingredients into the wet ingredients, mixing until just combined. Avoid overmixing to keep the muffins tender; a few lumps are okay.
Gently fold in 1¼ cups of chocolate chips into the batter.
Using an ice cream scoop or a large spoon, fill each muffin cup about ⅔ full with batter.
Sprinkle extra chocolate chips on top of each muffin for added chocolate flavor.
Bake in the preheated oven for approximately 30-35 minutes. Jumbo muffins may take a bit longer; check for doneness with a toothpick or cake tester.
Allow the muffins to cool in the tin for about 5 minutes, then transfer to a wire rack to cool completely.
Serve your delicious, moist, and chocolatey jumbo muffins as a breakfast treat or a delightful snack.
