Preheat the oven to 375°F (190°C). Line a jumbo muffin tin with 6 jumbo muffin liners or grease the tin well.
In a large bowl, sift together the all-purpose flour, unsweetened cocoa powder, granulated sugar, baking powder, baking soda, and salt. Mix well to combine.
In a separate medium bowl, whisk together the whole milk, vegetable oil, eggs, and vanilla extract until smooth.
Pour the wet ingredients into the dry ingredients and gently fold together using a spatula until just combined. Do not overmix; the batter should be slightly lumpy.
Fold in the 1 cup of semisweet chocolate chips evenly into the batter.
Divide the batter evenly among the 6 prepared jumbo muffin cups, filling each about 3/4 full.
Sprinkle the remaining 1/2 cup mini semisweet chocolate chips evenly on top of each muffin.
Bake in the preheated oven for 22 to 25 minutes, or until a toothpick inserted into the center of a muffin comes out with a few moist crumbs but no wet batter.
Remove the muffins from the oven and allow them to cool in the tin for 10 minutes.
Transfer the muffins to a wire rack to cool completely before serving.