Position a rack in the center of the oven and preheat to 400ºF. Place the butter in a 10-inch cast iron (or other oven proof) skillet and put in the oven to melt.
Combine the flour and salt in a large bowl, make a well, and add the eggs. Whisk to combine, adding the milk little by little until the batter is smooth. Whisk in the vanilla and about two-thirds of the melted butter. Set aside.
Heat the skillet with the remaining butter over a medium flame, and brush some of the butter around the rim of the skillet. Toss in the pears, cardamom, lemon juice and sugar. Cook, stirring occasionally, until the pears are tender and the sugars are beginning to caramelize, about 10 minutes.
Pour the batter into the hot pan over the pears and place in the oven. Bake until golden and dramatically puffed, as though trying to escape from the pan, about 25 minutes. Dust with powdered sugar and cut into wedges. Drizzle with maple syrup and serve immediately.
Leftovers, should there be any, reheat beautifully in a toaster oven in 5 or 10 minutes.
