Preheat oven to 350 degrees and oil a 9-inch glass pie plate.
Roast and peel poblanos. Wearing protective gloves, cut chiles into 1/2-inch dice. Melt butter. Into a small bowl sift together flour, salt, and baking powder. In a large bowl with an electric mixer, beat eggs until doubled in volume, about 3 minutes. Add butter, flour mixture, and cheeses and beat well. Stir in chiles and pour mixture into pie plate. Bake custard in middle of oven until top is puffed and golden brown and a tester comes out clean, 30 to 35 minutes.
Serve cheese puff immediately (it will fall slightly) with salsa.