1. Preheat the oven to 350° and grease a 9 x 13-inch baking dish with butter.  

2. Whisk the eggs together in a medium bowl. Add the milk, dill, salt, and pepper and whisk until well combined.

3. Pour the eggs into the prepared pan. Add dollops of cream cheese to the surface of the eggs and then arrange the smoked salmon evenly over the top.

4. Transfer to the oven and bake until the eggs are just set, approximately 25 minutes.

5. Cut the frittata into 6-8 pieces and serve immediately, garnished with red onion, capers, and optional dill.