Add the butter to a light-colored saucepan over medium heat. Cook, swirling occasionally, as the butter melts and begins to foam.

Continue cooking until you see golden brown bits forming at the bottom and the butter smells toasted and nutty, about 5–7 minutes.

Immediately pour the brown butter, including all of those flavorful brown bits, into a large mixing bowl. Let it cool for about 10–15 minutes.

In a separate bowl, whisk together the flour, baking powder, baking soda, and salt.

Add the granulated sugar and brown sugar to the cooled brown butter and whisk together.

Whisk in the eggs and vanilla, followed by the Greek yogurt, avocado oil, and milk.

Add the dry ingredients to the wet ingredients and gently fold everything together with a spatula until almost combined.

Fold in the chocolate chips. Stop mixing as soon as you no longer see streaks of flour. The batter will be very thick—this is exactly what you want.

Divide the batter between 6 greased or lined jumbo muffin cups. The cups should be almost completely full, with the batter slightly mounded in the center.

Let the portioned batter rest at room temperature for 20 minutes.

Preheat the oven to 425°F.

Right before baking, top muffins with coarse sugar.

Bake

Bake at 425°F for 5 minutes.

Without opening the oven door, reduce the temperature to 350°F and continue baking for approximately 22–25 minutes, or until the muffins are golden and a toothpick inserted into the cake portion comes out with a few moist crumbs.

Allow the muffins to cool in the pan for about 10 minutes before transferring them to a cooling rack.

Add a tiny sprinkle of flaky sea salt while they're still warm if you want