Warm the milk in a small saucepan until it bubbles, then remove from heat. In a small bowl, dissolve yeast in warm water. Let stand until creamy, about 10 minutes.
In a large bowl, combine milk, yeast mixture, butter, salt, sugar and flour. Mix thoroughly with rotary or electric mixer until batter is smooth. Cover and let stand at room temperature overnight.
The next morning, stir beaten eggs and baking soda into the batter; beat well.
Spray preheated waffle iron with non-stick cooking spray. Pour mix onto hot waffle iron. Cook until golden brown.
