Melt the chocolate in glass bowl or measuring cup in the microwave oven. Start with one minute on high. Stir the chocolate with a knife. Repeat the process in thirty-second bursts, stirring after each, until the chocolate is just barely melted and smooth.
While the chocolate is heating, cream the butter and sugar together
Add the amaretto to the mixer bowl. Sift the cocoa powder, baking powder and cornstarch together and add, in two portions. Beat in thoroughly.
Grind the almonds to a fine powder in a coffee mill. Add that to the bowl, then the egg yolkss. Continue to mix until well blended.
Scrape down the sides of the cowl until clean. While running the mixer on medium speed, slowly add the chocolate. Mix just until blended. DOn't overmix.
In a separate bowl, beat the egg whites with the cream of tartar until stiff but not dry. Fold this very gently with a rubber spatula into the mixer bowl.
Coat two nine-inch pie pans with shortening and fill them almost to the top with the batter. Bake in a preheated 275-300 degree oven for one hour. Cakes are done when the tops start to show small cracks. (This is normal.)
Allow cakes to cool on racks. Turn pans over onto plates. Dust the tops of the cakes with powdered sugar.