In an oven-safe skillet, heat olive oil over medium heat. Sauté the onion until translucent, stirring throughout (about 2 minutes). Add the smoked salmon and olives. Cook until the salmon is pink and opaque (about 2 minutes). Add salt and pepper to taste. Set aside.
In a medium bowl, whisk together eggs, cream and milk. Pour this mixture over the salmon mixture and stir to combine. Then, scatter the cubes of cream cheese over top of mixture. Sauté over medium heat without stirring until the edges appear firm (about 3 minutes).
Keeping the mixture in the skillet, place it in the oven. Bake until browned and puffy (about 20 minutes).
To serve, flip the frittata onto a serving plate and cut into wedges.