Preheat oven to 425ºF. Line 2 jumbo muffin pans with paper liners or spray with nonstick spray and set aside.
In a medium bowl, combine the flour, baking powder and salt. Set aside.
2 ¼ cups all-purpose flour, 1 tablespoon baking powder, 1 teaspoon kosher salt
In a separate bowl, add the cocoa powder and hot coffee and whisk to form a paste.
½ cup unsweetened cocoa powder, ½ cup hot freshly brewed coffee
To the bowl of a stand mixer, add the vegetable oil and brown sugar and beat on medium speed until blended, about 1 to 2 minutes (the mixture will resemble wet sand).
½ cup vegetable oil, 1 cup brown sugar
Add the cocoa paste and mix to combine.
With the mixer on low, add the milk, sour cream, beaten eggs and vanilla. Mix on medium speed just until combined.
1 cup whole milk, ½ cup sour cream, 2 large eggs, 1 tablespoon vanilla extract
With the mixer on low, slowly add the flour mixture to the wet ingredients, mixing until just combined. Do not overmix.
Stir in 1 cup of the chocolate chunks or chips.
1 ½ cups semi-sweet chocolate chunks or chocolate chips
Fill each cup of the muffin tin to the top. Sprinkle the tops with the remaining ½ cup of chocolate chunks or chips.
Bake for 5 minutes at 425ºF then lower the oven temperature to 350ºF and bake for 20-25 minutes (for jumbo muffins) or 18-22 minutes for (standard size), or until a toothpick inserted into the center of the center muffin comes out clean. *All ovens bake differently, so I recommend checking the muffins for doneness after 15 minutes.
Allow muffins to cool in the muffin tins for 5-10 minutes then transfer to wire racks to cool completely.