BLACKBERRY CAKE WITH MARSHMALLOW FROSTING

300g Président Unsalted Butter, softened, plus extra for greasing • 225g essential Waitrose Self-Raising Flour, plus extra for dusting • 5 large eggs • 300g Billington’s Golden Caster Sugar • 75g ground almonds • ½ orange, zest and juice • MARSHMALLOW FROSTING: 150g Président Unsalted Butter, softened • 250g icing sugar, sifted • ½ x 213g jar marshmallow fluff • 425g Waitrose 1 Blackberries • 4 tbsp Tiptree Blackberry Jelly* *Selected stores