Preheat your oven to 350°F and line a muffin tin with paper liners.
In a large mixing bowl, combine the flour, sugar, brown sugar, baking powder, baking soda, and salt. Mix well.
In a separate bowl, combine the melted butter, eggs, milk, and vanilla extract. Mix until well combined.
Slowly add the wet ingredients to the dry ingredients, stirring until just combined. Slowly fold in the chocolate chips. Be careful not to overmix.
To make the streusel topping, combine the flour, brown sugar, butter, and cinnamon (if using) in a small mixing bowl. Use your fingers or a fork to mix until the mixture resembles coarse crumbs.
Fill the muffin cups about 2/3 full with the batter. Sprinkle the streusel topping evenly over the muffins.
Bake for 18-20 minutes, or until a toothpick inserted into the center of a muffin comes out clean.
Allow the muffins to cool for 5-10 minutes before removing them from the muffin tin.