Preheat your oven to 350°F (175°C). This will ensure your frittata cooks evenly.
Heat a drizzle of extra-virgin olive oil in your 12-inch skillet over medium heat. Make sure to coat the bottom of the pan for even cooking.
Add the chopped onion and minced garlic to the skillet. Sauté for about 2-3 minutes, or until the onion becomes translucent. Next, add the chopped broccoli and cook for another 3-4 minutes until the broccoli is tender but still bright green.
While the vegetables are cooking, crack the 6 large eggs into a mixing bowl. Add the almond milk, sea salt, and freshly ground black pepper. Whisk together until well combined and slightly frothy.
Once the vegetables are ready, pour the egg mixture evenly over the sautéed vegetables in the skillet. Gently stir to combine, ensuring the vegetables are evenly distributed. Sprinkle the feta cheese on top.
Cook the frittata on the stovetop for about 2-3 minutes until the edges begin to set. This step helps to create a nice base before transferring it to the oven.
Transfer the skillet to the preheated oven and bake for 15-20 minutes, or until the frittata is puffed up and the center is set. A toothpick inserted into the center should come out clean.
Remove the frittata from the oven and allow it to cool for a few minutes. Slice it into wedges and serve warm, or let it cool completely to serve at room temperature.
