In a large bowl, combine sugar and sea salt.
Sift together flour, cocoa powder, baking powder and baking soda.
Toss chocolate chunks in the dry ingredients to prevent them from sinking during baking.
Make a well in the center of the dry ingredients. Add eggs and vanilla extract.
Add yogurt (or buttermilk) and cooled melted butter. Whisk vigorously.
Using a large spoon or spatula, gently mix until just combined. Avoid overmixing to keep muffins tender.
Cover the batter and refrigerate for at least one hour (or overnight) to ensure bakery-style high domes.
Preheat your oven to 425°F (220°C). Fill muffin cups ¾ full. Bake at 425°F for 6–10 minutes until muffins rise slightly above the muffin liners. Then reduce oven temperature to 350°F (175°C) without opening the oven door, and bake until muffins are crisp around edges and a toothpick inserted into the center comes out clean (about 25–30 minutes total).
Allow muffins to cool completely on a wire rack to prevent soggy bottoms.