Slow Cooker Banana Upside Down Cake

6 bananas, peeled and halved lengthwise 
5 Tbsp. butter, cubed
3/4 cup brown sugar
3 Tbsp. dark rum
1 box yellow cake mix
1/2 cup vegetable oil
3 eggs
1 tsp. vanilla
1 tsp. cinnamon
1/4 tsp. nutmeg

Place bananas, cut-side down, in a slow cooker lined with foil and sprayed with nonstick cooking spray. Top with butter, brown sugar and rum. Turn slow cooker to high.

In a large bowl, beat together cake mix, vegetable oil, eggs, vanilla, cinnamon and nutmeg. Pour batter over bananas and spread evenly with spatula. Layer paper towels over slow cooker then cover with lid. Cook on high about 3 hours, until browned slightly.

Turn off slow cooker and let set about 20 minutes. Use foil to remove cake and let cool about 30 minutes. Invert cake onto a platter and serve.