from an Austrian lady, Marika Kolinksy-Philips:
It is basically a chocolate butter cake with a chocolate glaze. So good. Have all ingredients at room temp.
4 T sweet butter
2 large eggs, separated
2/3 c sugar
1/2 t. vanilla
juice and grated rind of 1/2 lemon
1 c flour
2 t baking powder
2 T cocoa--unsweetened
2 t. instant coffee or espresso
1/2 c milk
1/3 c very fine dry white bread crumbs
3/4 c strained apricot jam
2/3 c chopped semi-sweet chocolate
3 T butter
1 c heavy cream whipped with 2 T vanilla sugar
Preheat oven to 350 degrees. Grease and breadcrumb an 8" springform pan. Tap pan to remove excess crumbs.
In a medium bowl, beat butter till fluffy. Add egg yolks and 1/2 the sugar and beat very smooth and creamy. Beat in vanilla, lenom juice and rind.
Sift flour with baking powder, cocoa, and instant coffee. Fold about 2/3 of this into the batter alternating with the milk. Beat smooth after each addition.
In a small bowl, beat the egg whites (using a pinch each of salt and cream of tartar) to stiff peaks, add the rest of the sugar a T. at a time and continue beating until very stiff and satiny.
Now gently fold the egg whites into the batter alternately with the rest of the flour. Spread smoothly into the springform and bake on middle shelf at 350 for 30-45 minutes (depending on pan size) or until done (use a tester).
Cool cake for 10 minutes then remove side from pan, and remove bottom.
Place cake on rack and cool completely. Slice horizontally into two even layers. (if the top is domed, carefully cut it to be flat first)
With cake still in wire rack, brush top of and sides of each layer with a bit of Kirsch(optional) then the apricot jam. If jam is too thick, heat it gently first. Replace top layer, and allow jam to completely dry before applying chocolate glaze. (I sometimes use a small folding Japanese hand fan to hurry this along)
Place chopped chocolate and butter in the top of a double boiler, over barely simmering water, stirring constantly. Remove from heat and beat vigorously with a wooden spoon or whisk until the chocolate thickens slightly, is very glossy and coats a spoon thickly. (should still be thin enough to por quickly) Pour over the entire cake and quickly smooth with a long thin offset icing spatula. Allow to set completely before cutting. (Use a long sharp knife and wipe the blade between cuts).
*If chocolate glaze loses its gloss, use a very fine brush dipped in cold water and brush over the top.
Place the whipped cream in a piping bag and decorate top with a few stars around the top edge if desired (though I don't know if this is traditional in Austria). Sachertorte is traditionally very plainly glazed but served with whipped cream piped against the side of a cut slice ("mit schlag"). Serve with a cup of rich, strong coffee.
I hope you try this, it is very straighforward, and I've used it many times for a birthday cake.