Mix the softened butter with the powdered sugar and vanilla, beat with a mixer until creamy; add the egg yolks 1 by 1 during beating.
Beat the egg whites with a pinch of salt to snow using a mixer and add the sugar in 6 lots, beat to stiff snow.
Melt the 74% cocoa dark chocolate in a water bath, add it to the butter-egg yolk mixture.
Add the butter-chocolate mixture to the egg whites, add the flour and baking powder and carefully beat with a whisk or silicone spatula until homogeneous.
Pour the dough into a 10 1/4″ (26 cm) diameter form, laid out with baking paper, with sides smeared with butter.
Bake at 356°F (180 °C) for 15 min, at 338°F (170 °C) for 15 min and then at 320°F (160 °C) for 15 min. Take it out and cool.
Cut the cake layer into 2, through the middle, smear 1 half with half the jam, place the 2nd half on top and smear with the remaining jam all over. Leave it for 30 min. to dry. You need to heat the jam a little and pass it through a sieve.
For the soft chocolate glaze, make a syrup from the water and sugar by putting them to boil until the sugar dissolves. Add the 58% cocoa dark chocolate to the syrup. Stir until the chocolate melts. While the glaze is still hot, pour it over the cake, drain off any excess.
Place the cake onto a platter with a round crochet napkin.
Use the couverture chocolate to write the word Sacher in the middle of it.