Preheat oven to 400°. Place butter in a 12-in. cast-iron or other ovenproof skillet. Place in oven until butter is melted, 4-5 minutes; carefully swirl to coat evenly. , Meanwhile, in a blender, process eggs, ricotta, milk, vanilla and lemon zest until blended. Add flour, sugar, baking powder and salt and process until blended. Pour into hot skillet. Top with berries., Bake until puffed and sides are golden brown and crisp, 25-30 minutes. Remove pancake from oven; serve immediately with confectioners' sugar.