The rum will ignite when you tilt the pan; this burns off the alcohol.
1/2 cup packed brown sugar
1/4 cup unsalted butter, divided
1 vanilla bean, split lengthwise
6 (1/2-inch-thick) slices fresh pineapple
1/4 cup dark rum
5 ounces gluten-free multipurpose flour (such as King Arthur Flour; about 1 cup)
1/4 cup almond flour
1/2 teaspoon baking powder
1/2 teaspoon kosher salt
1/4 teaspoon baking soda
1/2 cup light sour cream
2 tablespoons canola oil
2/3 cup granulated sugar
2 large eggs
How to Make It
Preheat oven to 350°.
Combine brown sugar, 2 tablespoons butter, and vanilla bean in a large skillet over medium heat; cook 6 minutes or until butter melts and sugar dissolves, stirring frequently. Add pineapple in a single layer. Carefully pour rum over pineapple; tilt pan to ignite. Simmer 5 minutes on each side or until slightly tender and caramelized. Remove vanilla bean.
Coat a 9-inch cake pan with cooking spray. Arrange pineapple in a single layer in bottom of pan; pour sugar mixture over pineapple, tilting pan to coat bottom evenly.
Weigh or lightly spoon multipurpose flour into a dry measuring cup; level with a knife. Combine multipurpose flour, almond flour, baking powder, salt, and baking soda; stir with a whisk. Melt remaining 2 tablespoons butter in a microwave-safe dish at HIGH for 35 seconds. Place melted butter, sour cream, and oil in a bowl, stirring well with a whisk.
Place granulated sugar and eggs in a large bowl; beat with a mixer at high speed 5 minutes or until fluffy. Reduce speed to medium. Add flour mixture and sour cream mixture alternately to egg mixture, beginning and ending with flour mixture. Spoon batter over pineapple, spreading evenly. Bake at 350° for 38 minutes or until a wooden pick inserted in center comes out clean. Cool in pan 15 minutes on a wire rack. Loosen cake from edges of pan with a knife; invert onto a plate.