For the Pear Topping:

1. Melt the butter in the bottom of a 10-inch cast-iron skillet. Add the brown sugar and stir to combine. Once the mixture bubbles slightly, whisk in the salt, vanilla, and cardamom. Remove from heat.
2. Carefully arrange the pear slices in a circular pattern in the brown sugar-butter mixture, being sure to cover the entire bottom surface of the skillet.

For the Batter:

1. Preheat the oven to 350°F. In a medium bowl, whisk together flour, baking powder, salt, and spices. Set aside.
2. In the bowl of a stand mixer, cream together the butter and sugars until light and fluffy. Add vanilla extract; beat to combine. Add egg yolks, one at a time, beating to combine.
3. Alternating with the milk, gradually add the flour mixture to the butter mixture, and mix, on low speed, just until the flour is incorporated.
4. In a large bowl, beat reserved egg whites and the cream of tartar with a hand mixer until stiff peaks form. Gently fold the egg whites into the batter.
5. Pour the batter into the skillet, spreading the batter evenly over the pears and being careful not to disturb the pattern.
6. Bake for 40-45 minutes or until the top is golden brown and a cake tester inserted into the center of the cake comes out clean. Run a sharp knife around the inside edge of the skillet and immediately (and carefully!) invert the cake onto a serving dish or cake stand. Allow to cool slightly before slicing and serving with vanilla ice cream.