Preheat oven to 350 F. Lightly butter a 9-1/2 inch round cake pan. Pour melted butter into the bottom of the pan and sprinkle evenly with brown sugar and chopped macadamia nuts. Arrange pineapple rings evenly in the bottom of the pan. Set aside.
In a mixing bowl, using a hand or stand mixer, cream together butter and sugar until light and fluffy. Add eggs one at a time, beating thoroughly between each addition. Scrape down the sides of the mixing bowl with a spatula as needed. Add vanilla and combine.
Sift together dry ingredients into small bowl. Alternating between the milk and dry ingredients, slowly add to butter mixture. Once all of the dry ingredients and milk are added, increase speed to high and beat for 2 minutes.
Pour batter over pineapple in prepared pan. Bake in prepared oven 35 to 45 minutes or until a toothpick inserted near the center comes out clean.
Remove from oven and let cool 15 minutes in the pan on a wire rack. Run a knife around the edge of the cake. Invert a serving plate over the top of the pan, and flip to remove the cake from the pan. Lift off the pan, and scrape any remaining syrup in the pan over the cake. Serve warm or at room temperature. Makes 8 to 10 servings.