Preheat the oven to 450*F. In a small bowl, combine the thyme, lemon zest, and Parmesan cheese. Mix and set aside.
Place 2 tablespoons butter in a cast-iron skillet. Put the skillet in the oven for 2 minutes or until butter is melted. Carefully remove the hot skillet from the oven, swirl to fully coat the bottom with melted butter, and set aside.
In a separate small saucepan, melt the remaining 2 tablespoons of butter. In a blender, combine the melted butter, eggs, milk, flour, salt, and pepper. Blend until smooth.
Pour the batter into the hot skillet. Sprinkle with the Parmesan mixture. Return to the oven and bake for 20 minutes or until puffed and golden.
Remove from the oven and top with smoked salmon before serving.