How to Make It
In a 10-inch cast-iron skillet, melt 2 Tbsp. butter over medium heat. Add berries, sugar, pomegranate juice, 1/2 tsp. vanilla and 1/4 tsp. salt. Bring to a simmer and cook, stirring occasionally, until liquid is reduced and coats the back of a spoon, about 35 minutes. Remove from heat and let cool. Refrigerate in skillet until chilled, 4 hours to overnight.
Preheat oven to 350°F. In a medium bowl, whisk together flour, baking powder and 1 tsp. salt. In a large bowl, using an electric mixer on medium speed, beat 15 Tbsp. butter with brown sugar and 2 tsp. vanilla until fluffy, about 3 minutes. Add eggs 1 at a time, beating well after each; beat in sour cream. Stir in dry ingredients until just combined.
Spread batter evenly over chilled strawberry mixture. Bake until a toothpick inserted into center comes out clean, about 45 minutes.
Transfer skillet to a wire rack and let cool for 10 minutes. Run a knife around edge of skillet to loosen cake. Invert skillet onto a plate, unmold cake and let it cool completely.