Preheat your oven to 350°F (175°C) and grease a 9-inch round cake pan with unsalted butter.

Melt 3/4 cup of unsalted butter in a medium saucepan over medium heat and stir in 1/2 cup of brown sugar until combined. Pour into the prepared pan.

Arrange 6 pineapple rings on top and sprinkle 3/4 cup of cranberries around them.

In a large mixing bowl, whisk together 1 1/2 cups of flour, 1 1/2 tsp of baking powder, and 1/2 tsp of salt.

Cream together 3/4 cup of granulated sugar and the melted butter mixture until light and fluffy. Add 2 eggs and 1 tsp of vanilla, mixing until smooth.

Gradually add the flour mixture and 1/2 cup of pineapple juice alternately, beginning and ending with the flour. Fold in 1/4 cup of sour cream.

Pour the batter over the fruit in the cake pan and bake for 40-45 minutes until a toothpick comes out clean.

Let the cake cool in the pan for about 10 minutes, then invert onto a serving plate.

Serve warm or at room temperature, optionally with vanilla ice cream or whipped cream.