Mix the melted butter and brown sugar and stir until smooth.
Spread an even layer over the bottom of the pan.
Lay the pineapple slices in a single layer over the bottom.
Put a cherry in the center of each with the cut side up.
Sprinkle with nuts.
Whip egg whites and cream of tartar until stiff but not dry.
Beat sugar and yolks until thick and lemon yellow.
Add in the reserved pineapple juice, flavoring, and rum if using.
Sift flour, salt and baking powder together.
Blend into the egg yolk mixture until smooth.
Make sure the batter is well blended before adding egg whites.
Fold in ½ the egg whites carefully but thoroughly.
Fold in the remaining egg whites.
Spoon over the pineapple and bake at 350F for 30 minutes.
Allow to cool 5 to 10 minutes before inverting on large platter.
Fold the egg whites in very, very gently so they don't deflate.This keeps your cake light and airy.
If you overcook the cake it will taste like stale cardboard. Watch it carefully.
Let the cake cool for about 5 minutes before turning out of the pan. The sauce needs to thicken up or it will run all over.
Use good pineapple, the final product depends on it. Most vintage recipes assume pineapple in heavy syrup is being used. Adjust sugar to your own tastes. (I think it's better with the pineapple in heavy syrup.)