Preheat oven to 350°. Arrange pineapple in a single layer in a well seasoned 12-in. cast-iron or other ovenproof skillet., In a large bowl, cream butter, coconut oil and sugar until light and fluffy, 5-7 minutes. Add egg yolks, 1 at a time, beating well after each addition. Beat in coconut extract. In another bowl, whisk flour, baking powder and salt; add to creamed mixture alternately with coconut milk, beating well after each addition., With clean beaters, beat egg whites and cream of tartar on high speed just until stiff but not dry. Fold a fourth of the egg whites into batter, then fold in remaining egg whites. Spread over pineapple. Bake until a toothpick inserted in center comes out clean, 55-60 minutes. Cool 10 minutes before inverting onto a serving plate. Serve warm, with toasted coconut if desired.