For the Sacher cubes or Sacher slices, prepare the dough as described for the Sacher cake.
Preheat the oven to 200 °C convection oven. Grease a baking tray well with clarified butter and sprinkle with flour. Knock out any excess flour.
Spread the mixture on a surface of about 30 x 24 cm about 2 cm high. (To do this, border the surface with double or triple folded aluminum foil.) Place in the oven and bake for about 10-15 minutes. Remove and let cool briefly.
Meanwhile, vigorously heat the strained jam and spread until smooth.
Spread sponge cake base thickly with jam, cut in half widthwise and fold on jam side. Immediately place in the refrigerator (or preferably the freezer) so that the mixture stays really moist.
Then cut into about 3 x 3 cm cubes or slice shape, trimming the edge nicely all around beforehand.
Now dip (or brush) each cube in hot jam, place on a cooling rack and let dry for 1 hour.
Meanwhile, for the glaze, bring sugar and water to a bubbling boil for 5-6 minutes, then let cool slightly. Melt chocolate in bain-marie and gradually mix with sugar solution, stirring, until a thick, smooth glaze forms. Stir in warmed jam.
Coat cubes with glaze, again carefully and quickly smoothing with a palette. Allow Sacher cubes to dry and place in decorative paper sleeves or place the sch