Let the eggs and milk stand at room temperature for 30 minutes. Heat the oven to 425 degrees. Add the apple slices, 2 tablespoons sugar, and 1/4 teaspoon cinnamon and toss to coat.
Put the butter in the cast iron skillet and put in the oven for 2 minutes.
Take the skillet out swirl the melted butter around the pan, and add the apple mixture.
Bake for 10 minutes or until the apples begin to soften and the butter is bubbly.
While the apples are cooking, add the eggs, milk, flour, vanilla, salt, and remaining sugar and cinnamon to the blender. Blend for 1 minute, or until frothy.
Pour the batter over the hot apples.
Bake for 25 to 30 minutes or until puffy and golden brown.
Make the yogurt cream by mixing together yogurt, maple syrup, cinnamon, and vanilla.
Dust popover with powdered sugar and cut into wedges. Serve with yogurt cream.