Cut off the top (stem) of each pepper and save the tops for later.
Using a small teaspoon, remove the seeds from each pepper. Wash and dry the inside of the peppers to remove any remaining seeds.
Place the peppers into a bowl in an upright position so that they are easy to grab and fill and the hollowed opening is facing upwards. Add a pinch of salt into each pepper and a cube of the butter.
In a separate bowl, whisk the eggs. Add the feta and tomato, if using. Mix well until fully combined.
Add 2 tablespoons of the feta filling into each pepper. There should be a little bit of room at the top, as the filling will expand as it bakes, so fill them no more than ¾ of the way.
Line a baking dish with parchment paper and arrange the stuffed peppers side by side. Gently replace the stems onto each pepper to help prevent the filling from spilling out during baking. (Some of the filling may come out a little as they bake which is okay so don’t worry.)
Sprinkle the peppers with salt and add a drizzle of olive oil. Using a fork, gently poke each pepper on top so that the air can escape as they bake. This method will prevent them from cracking.
Bake, uncovered, for 35 to 45 minutes depending on the oven. Bake time will depend on your oven and the type of dish you use, so keep an eye on the peppers, to check for doneness around 30 minutes. If your oven is strong, you can bake at 400F (200C). My oven is very weak so I increase the heat.
Once the peppers are soft and browned on top, they’re ready. Enjoy them as is, or topped with tomato sauce or marinated in olive oil and freshly chopped dill!