Preheat oven to 350 degrees. Lavishly butter a loaf pan. Heat a kettle of water to boiling and set aside.
In a small bowl, crack 4 eggs and whisk together gently. Pour the beaten eggs into the buttered loaf pan. Sprinkle with salt and pepper. Arrange the asparagus, lengthwise in the loaf pan. Sprinkle ½ cup cheese and several fresh tarragon leaves over the asparagus.
Crack and beat 4 more eggs. Pour them over the asparagus and cheese in the loaf pan. Sprinkle with salt and pepper. Arrange the tomatoes over the eggs, sprinkle ½ cup cheese over the tomatoes, and sprinkle a few more leaves of tarragon.
Crack and whisk the remaining 4 eggs. Pour over the tomatoes in the loaf pan. Arrange the onion slices over the eggs, and sprinkle the last ¼ cup cheese over the onions. Cover the loaf pan tightly with aluminum foil.
Place the loaf pan into a larger baking pan, and fill larger pan with boiling water until it comes to about ½ way up the loaf pan.
Bake for 1 hour, remove foil lid, and bake for additional 10 minutes, until the top is golden. Serve warm or cold.
Notes
Adapted from Little Flower: Recipes from the Cafe by Christine Moore.
Recipe by The Domestic Front at https://www.thedomesticfront.com/egg-terrine/