Set your oven to 375°F to ensure it’s at the right temperature by the time your egg mixture is ready.
Using a skillet, precook the sausage over medium-high heat until it's thoroughly cooked and crumbled into small pieces. This step is crucial for evenly distributing the sausage mixture in your egg muffins.
In a large mixing bowl, crack the 12 large eggs and whisk them until they’re thoroughly scrambled. This ensures fluffy eggs and a uniform texture in your muffins.
Add the cooked sausage, fresh spinach, whole milk, garlic powder, onion powder, salt, black pepper, and Mexican blend cheese to the large bowl with the eggs. Mix well to combine all ingredients evenly.
If you're not using silicone muffin liners, lightly grease the muffin tin with cooking spray or olive oil to prevent sticking. For best results, use silicone liners, which makes removing the muffins a breeze and keeps cleanup minimal.
Use a ¼ measuring cup to scoop out the mixture. Fill the ¼ measuring cup just slightly under full with the egg mixture and pour into the muffin cups. This method ensures that each muffin is perfectly portioned and bakes evenly.
Place the muffin tray in the preheated oven and bake for 15-20 minutes. The egg muffins should have lightly golden brown edges and spring back to the touch when done.
Once your egg muffins finish baking, remove them from the muffin tin immediately to prevent sweating and overcooking. Let them cool on a cooling rack before storing them in an airtight container. You can reheat these breakfast muffins in the microwave for about 15 seconds each for a quick breakfast on busy mornings.