Place a rack in the centre of your oven and preheat oven to 375ºF.
In a saucepan over medium high heat, melt butter. Stir the butter occasionally so it cooks and browns evenly. When the butter starts to smell nutty and is browned remove it from the heat, transfer it to a bowl and let it cool.
In a large bowl, whisk together the flour, brown sugar, baking powder, cinnamon and salt.
In a separate bowl, whisk together the milk, eggs and vanilla.
Add the wet mixture and the melted and cooled browned butter to the dry ingredients and mix until just combined. Stir in the chocolate chips. Don't over-mix the batter or you will have tough muffins.
Evenly spoon the batter into the greased or paper-lined muffin cups, filling almost to the edge of the muffin cups.
Bake until a toothpick inserted in the centre of the muffin comes out clean about 18-20 minutes.
Let the muffins cool in the pan on a rack for 5 minutes before removing them and placing onto a wire rack to cool completely.
Muffins can be stored in an airtight container for up to 3 days or frozen for later consumption.