Preheat oven to 350 degrees. Butter 8 in round cake pan with two inch sides. Line bottom with parchment or waxed paper and butter again.
Blend sugar and almond paste in processor til finely ground.
Put flour, salt and baking powder into small bowl and whisk to blend.
Using electric mixer, beat butter, sugar and almond paste on medium speed until light and fluffy, about 3 minutes.
Add eggs one at a time, beating on medium high until each is incorporated.
Fold in dry ingredients and transfer mix to pan.
Bake for 40 minutes without opening oven, rotate pan and bake until cake is golden and firm to the touch. (Another high altitude change...I only baked mine for at most 35 minutes total).
Cool in pan for 10 minutes, run knife around outer edge, invert cake onto flat surface and remove paper from the bottom. Turn over and cook on rack.
Cut cake in half horizontally using a long serrated knife (bread knife is perfect).
Using the bottom of a tart pan, transfer the top half of the cake to a work surface.
Put remaining piece of cake, cut side up, on cake plate and spread the surface with jam. Place top half of cake on top of jam, cut side down.
Dust with confectioner's sugar and served with lightly sweetened whipping cream NOTE: To evenly cut the cake, measure the overall height. Then mark the halfway point with toothpicks at several points all around the cake. Use these toothpicks as your guide to slowly cut the cake in half with a serrated knife.