If you prefer a fruit topping, such as the one below, let your cake sit and allow to cool down.
In a small casserole, heat the frozen fruits with a little lemon juice, 1 tbsp water & the suggar (if added). Let the berries simmer for a couple of minutes, until soft & juicy.
Next, add the gelatine sheets to cold water (or follow instructions on back). Leave them in for 5 minutes.
While waiting for the gelatine, you might want to strain the berries, as the berry glazing will become much nicer without all the seeds. Really get into it though, as not to waste anything. (I used the remainders, including the seeds, in my porridge the next morning - no need to waste it!)
Once strained, pour back into the casserole & add the gelatine. Mix until fully incorporated & add to the cake. Either leave the cake in the tin, so nothing will run down the sides or be really, really careful. The higher the glazing, the yummier - for me at least.
Store in the fridge for at least 2 hours or overnight.