Combine milk and apple cider vinegar. Allow to set for at least 5 minutes. Make sure egg has been removed from the refrigerator and allowed to come to room temperature.

In a small dish, melt butter and allow it to cool. 

In a large bowl, combine flour, sugar, baking powder and salt. 

To the dry ingredients, add curdled milk, egg, and melted and cooled butter. Mix until thoroughly combined. Allow to rest for at least 5 minutes. Meanwhile, plug in / turn on waffle maker to warm.

Cook waffles according to waffle maker directions. Once cooked, keep warm in oven set at 200 degrees. 

While the waffles are cooking, prepare the chicken. Either thinly slice a regular chicken breast, or purchase thinly sliced breasts and pound them until flat. 

In a wide, shallow bowl, whisk one egg. In a quarter sheet pan (or cookie sheet) pour rice flour on one side and bread crumbs on the other. 

Coat raw chicken breast in rice flour. Then dip both sides in egg. Make sure excess has dripped off. Then, coat each side with bread crumbs. Place coated chicken on plate while coating the remaining breast pieces. 

After waffles are finished cooking, cook the breaded chicken. I cook mine in my Cuisinart Standard Waffle Maker, on level 3, for 3 minutes. The chicken will not need to be flipped, as the waffle maker is cooking it from both sides. 

To build sandwich, place one piece of cooked, breaded chicken on half of waffle. Top with spinach or desired toppings (such as the sauce above), then top with remaining half of waffle. Cut down the center and enjoy!