Pour the mixture into an oiled, medium-sized, round tray. Bake in a preheated 392°F (200 °C) strong oven. Check with a toothpick to see if it''s ready.
Be careful not to burn it because it bakes quickly. During baking, the cake will crack slightly on top but that's not an issue because you'll be glazing it later anyway.
In a casserole on the stove, put the ingredients for the syrup to boil but without thickening. Leave to cool well and pour the cold syrup over the cooled cake layer. It's important for both the cake layer and syrup to be completely cold.
Now get to preparing the buttercream. First, beat the butter and powdered sugar, then add the yolk and vanilla. Beat all this with a mixer and smear it onto the syruped cake.
The last step is to make the caramelized sugar. Caramelize the sugar in a dry pan to a light-colored caramel, add the walnuts and mix well. Pour it onto aluminum foil and wait for it to harden. Break it apart into small pieces and mash before sprinkling over the cake (I mashed them with a meat mallet).
Source: Tsvetomira Ivanova.