Warm milk in a small saucepan until it bubbles, then remove from heat.

Dissolve yeast in warm water in a small bowl. Let stand until creamy, about 10 minutes.

Combine milk, yeast mixture, butter, salt, sugar, and flour in a large bowl. Mix thoroughly with an electric mixer until batter is smooth. Cover and let stand at room temperature overnight.

The next morning, preheat a waffle iron.

Stir beaten eggs and baking soda into batter; beat well.

Spray the hot waffle iron with nonstick cooking spray. Pour mix onto waffle iron and cook until golden brown.