In a 25cm oven-proof frying pan (cast-iron works great), melt butter over very low heat. Remove from heat, and sprinkle brown sugar evenly over pan. Arrange pineapple slices to cover bottom. Distribute cherries around pineapple.
Sift together flour, baking powder and salt in a bowl.
Separate the eggs into two bowls. In a large bowl, beat egg whites just until soft peaks form. Add caster sugar gradually, beating well after each addition. Beat until stiff peaks form.
In a small bowl, beat egg yolks at high speed until very thick and yellow. With a spatula, using an over-and-under motion, gently fold egg yolks and flour mixture into whites until blended.
Fold in melted butter and almond extract. Spread batter evenly over pineapple in frying pan.
Bake for 30 to 35 minutes or until surface springs back when gently pressed with fingertip. Loosen the edges of the cake with knife. Cool the cake for 5 minutes before turning it out onto a serving plate.