Preheat the oven to 350ºF.
Place baking parchment in the bottom of a spring form pan. Spray the sides of the pan with cooking spray.
Wash the whole orange under hot water. Dry off and gently peel as to not damage the flesh or peel. Cut the orange peel into small strips. In a bowl, mix the orange peel and cane sugar. Set aside.
Juice the orange and place freshly-squeezed orange juice in a cup.
Crack eggs, separating whites from yolks, into two small bowls. Vigorously whisk the egg whites until stiff. Add the orange juice and buckthorn berry juice to the egg yolks, mixing well. Add the beaten egg whites to this mixture.
Combine the ground almonds with the powdered sugar and add to the egg mixture. Using a spatula, gently fold everything together.
Pour the batter into the prepared spring form pan. Bake in the oven for 30 minutes.
While baking, heat up the orange marmalade in a small saucepan. Remove the cake from the oven after it is finished baking and spread on the liquid orange marmalade. Lastly top the cake with the sugared orange peel strips. Allow cake to cool.