Melt butter in a large saute pan set to medium-low heat.
Add sliced onions, 1/4 teaspoon of salt, and a pinch of pepper. Cook onions for 15-20 minutes until caramelized.
Add 2-3 tablespoons of water every few minutes to prevent burning.
Preheat oven to 375 and line the bottom of large sheet pan with parchment paper. Coat sides with non stick spray.
Sprinkle sheet pan with cooked onions.
Add eggs, egg yolks, remaining salt, pepper, coconut flour, and spinach to a high speed blender. Mix on high until combined.
Pour mixture into sheet pan over onions.
Bake for 22-24 minutes until eggs are set in the middle.
Cut into shape using cookie cutters if desired.
Serving Size - 3 small pieces (makes 21 pieces). Per Serving: Calories - 134 kcal, Protein - 12g, Total Carbohydrate - 3g, Total Fat - 8g, Fibre - 1g.