Preheat the oven to 356°F (180 °C). Grease a tray and sprinkle it liberally and evenly with 4 tablespoons brown sugar. Arrange the bisected and drained of juice apricots along the bottom with the flat sides down.
For the layer, beat the butter and remaining brown sugar until you get a fluffy cream. Add 1 cup apricot jam or marmalade. While stirring, add the eggs one by one, then the grated orange peel and juice. In a separate bowl, combine the sifted flour, ground walnuts, baking powder and salt. Add the dry ingredients to the liquid mixture.
Mix by hand until the mixture becomes homogenized. Then pour out the dough over the apricots in the tray. Put the cake to bake for 30 to 40 minutes.
Let the finished cake cool and flip it over onto a platter. Using a brush, smear the top with a little apricot jam to get a nice glazed look.