Preheat oven to 425 degrees and line a muffin tin with muffin cups. First, make the streusel topping. In a small bowl, combine the brown sugar, granulated sugar, all purpose flour and butter and mix with your hands until combined. It will be crumbly. Set aside.
In a large bowl, whisk together the flour, baking powder, baking soda and salt. Set aside. In a separate bowl, whisk together the melted butter, both sugars, and eggs. Then add the vanilla extract, buttermilk and yogurt and mix until combined. Pour the wet ingredients into the dry ingredients and mix until just combined. Add chocolate chips and mix until incorporated. Do not over-mix. Portion out the batter into the prepared muffin tin. Top with the streusel.
Allow the muffins to bake for 5 minutes at 425 degrees, then, without opening the oven door, reduce the temperature to 350 degrees and continue to bake for another 12-17 minutes. The muffins are finished when a toothpick comes out clean. Enjoy!