Blood Orange Thyme Upside Down Cake

4-5 blood oranges

3/4 cup (6 oz, weight) butter, softened and divided

1/2 cup brown sugar

2 cups all-purpose flour

2 teaspoons baking powder

1/2 teaspoon salt

1 cup granulated sugar

1 teaspoon dried thyme

1/2 teaspoon ground ginger

2 large eggs

1 teaspoon vanilla extract

1/2 cup whole milk

Preheat oven to 350-degrees F. Grate 1 T. of zest from oranges. Cut off tops and bottom of oranges. Carefully cut off rinds and pith of oranges from top to bottom, following curve of orange. Thinly slice oranges and remove any seeds. Set aside. Melt 1/4 cup butter in a 9-inch round or 9×9-inch square baking pan in oven until melted. Carefully remove from oven. Whisk brown sugar into melted butter until combined. Place back in oven for 3 minutes. Remove from oven and whisk slightly to blend; spread evenly across bottom of pan. Arrange blood orange slices evenly over top of butter/sugar. Reserve any extra slices for garnish. Set aside. In a bowl, whisk together flour, baking powder and salt. Set aside. In a separate mixing bowl beat together remaining 1/2 cup softened butter, granulated sugar, orange zest, thyme and ground ginger until slightly lightened in color, about 3 minutes. Scrape down bowl as needed. Add eggs one at a time, beating well after each addition. Scrape down bowl as needed. Beat in vanilla extract until smooth. Alternate adding in flour/baking powder mixture and milk, mixing until just combined. Scraping down bowl as needed. Carefully spoon batter over blood orange slices in baking pan and gently spread evenly. Bake at 350-degrees F until wooden pick or cake tester comes out clean, about 35-45 minutes. Let cool in pan for 10 minutes then invert onto serving plate. Scrape out any remaining syrup from pan and drizzle over cake. Serve with fresh whipped cream or vanilla ice cream.