Preheat oven to 425℉. Prepare your muffin pan by placing muffin liners in every other muffin cup. In a microwave-safe bowl, melt the butter in the microwave in 30-second increments until completely melted. Add the melted butter to a large mixing bowl, along with the granulated sugar and brown sugar. Whisk the ingredients together until fully combined.
Mix in the eggs one at a time. Add the vanilla extract, buttermilk, and sourdough discard. Use a rubber spatula or wooden spoon to gently combine the ingredients.
Add the flour, baking powder, baking soda, and salt, mixing until just combined. Gently fold in the chocolate chips. Allow the muffin batter to rest for 20-30 minutes on the counter.
When you're ready to bake the muffins, pour the batter into the muffin tins. Use a 1/4 cup measuring cup to easily pour the batter into every other muffin cup, filling them to the top. Keeping them separated by every other muffin cup allows the muffins to puff up and not spread on to each other.
Bake the muffins at 425℉ for 10 minutes. After 10 minutes, lower the temperature of the oven to 350℉ without opening the oven door. Let them bake for another 10-13 minutes. Stick a wooden toothpick in the center of a muffin to check if they are done baking. If moist crumbs stick to the toothpick, they are ready to come out of the oven. The tops of the muffins will also be golden brown. If there is wet batter sticking to the toothpick, the muffins need to bake longer.
Once removed from the oven, allow the muffins to sit in the muffin tin for about 10 minutes before transferring to a wire rack to cool further. Serve warm with a pad of butter! Enjoy!