Preheat oven to 350 degrees F.
Start by frying the bacon. While the bacon is cooking, prepare the other ingredients. Dice or slice the onion, chop spinach, grate cheese, and break up goat's cheese into small pieces.
6 slices bacon, cooked and broken or cut into pieces
Whisk together the eggs, sour cream, salt, and pepper until a smooth texture is reached. Set aside.
12 large eggs, 1 cup sour cream, ½ teaspoon salt, ¼ teaspoon black pepper
Remove bacon from the pan onto a paper towel-lined plate. Remove all but 2 tablespoons of bacon fat.
Fry onion in bacon fat on medium heat until they are soft and caramelized, stirring often. This will take 8-10 minutes to produce the sweet caramelization. Reduce heat if they are starting to get too dark. See photo above.
1 medium white onion, sliced or diced
Add the tomatoes, bacon, and spinach. Stir to combine.
2-3 cups baby spinach
Turn the heat off and pour in the egg mixture. Carefully stir it around to disperse the ingredients evenly.
Drop the pieces of goat's cheese evenly over the frittata, then add the grated cheddar.
140 g goat cheese (chevre), 1 ½ cups aged cheddar, shredded
Bake in preheated 350 F oven for 20 to 30 minutes or until the frittata is set in the center.
If you wish to brown the cheese on top, set the broiler on high and place frittata on the top rack. Keep a close eye on it until the top is as browned as you like.
Serve immediately or let sit until it's room temperature.