Melt butter over medium heat in a medium-sized saucepan, stirring often, until butter foams and then browns (do not burn), 5 - 8 minutes. Transfer to a mixing bowl and let cool.

Whisk milk, buttermilk, sugar, yeast, and salt in a large mixing bowl. Whisk in flour and cooled brown butter.

Cover and let batter sit at room temperature at least 8 hours and up to 12 hours.

Once the 8 hours is up, whisk in eggs and baking soda.

Heat waffle iron until very hot. coat iron with nonstick spray and pour batter onto waffle iron, spreading it to cover surface. Cook until golden brown and cooked through.

Serve immediately with butter and maple syrup.