In a medium bowl, whisk together the eggs, liquid egg whites, Greek yogurt, sea salt, and black pepper until the mixture is smooth and well combined.
Toast the sourdough bread slices in a toaster or under a broiler until they reach a golden, crisp texture.
Heat a non-stick skillet over medium-low heat and melt the grass-fed butter, swirling to coat the surface of the pan.
Add the baby spinach to the skillet and sauté for approximately 1 minute until the leaves are just wilted.
Pour the egg mixture into the skillet over the spinach, allowing it to sit undisturbed for 20 seconds to begin setting.
Using a silicone spatula, gently push the eggs from the edges toward the center, creating soft, large curds.
Continue cooking the eggs low and slow, stirring occasionally until they are mostly set but still appear slightly moist.
Remove the skillet from the heat immediately to prevent overcooking from residual heat.
Plate the scrambled eggs alongside the toasted sourdough, garnish with freshly chopped chives, and serve warm.