Slightly problematically sugar-free beetroot, raspberry and chocolate cake

These raspberries are not ripe yet. I picked all the ripe ones for my cake.

I was in two minds whether to include this recipe, because it's somewhat problematic. The problem is that I made it free from added sugar, because I try to avoid added sugar, and when you eat it like that, the cake is weirdly moreish, but also an intense-cocoa-powder experience that is probably too much for most people and made me think I shouldn't make this cake again, despite its perfect moist texture and weird moreishness (it really is weird, I spent my whole time eating it thinking I wasn't keen on the flavour, but I really wanted some more).

My other half has no such qualms about sugar, so I covered his slice in maple syrup, and he said it was restaurant-quality food and I had to put the recipe on the blog (and he is not a man afraid to say when he thinks my cooking experiments haven't worked out).
I suspect the correct answer is to include sugar or your favourite sugar substitute in it while baking it. I'm not entirely sure how much. Based on the recipe I adapted this from, my guess would be 250 g of caster sugar, but I haven't tried this, so can't be certain it doesn't change the recipe, for instance changing the delicious moist texture my other half loved so much. I was hoping the raspberries and beetroot would together be sweet enough to make the cake palatable, but even in my world of thinking most things are sweeter than everyone else because I barely eat sugar, I found this bitter. Interestingly, my other half didn't find his single mouthful of un-syruped cake bitter, so whether you find such highly chocolatey but unsweetened cakes bitter may depend on your genes. It's quite possible I'm something of a supertaster.
A lot of the quantities in this recipe are based on how much I happened to have easily available from the garden (the raspberries were all my ripe raspberries). Generally people say you're not supposed to mess with baking recipes, as they can go horribly wrong, but I've often found that if I change the amount or type of fruit in them, I mainly end up having to adapt the baking time and don't ruin anything critical.
Anyhow, here's the recipe, feel free to run your own experiments from it:

Slightly problematically sugar-free beetroot, raspberry and chocolate cake

275 g cooked beetroot (chop into 4 pieces and boil for 30 mins to cook if not buying pre-cooked)
3 medium eggs
200 ml mild olive oil (the sort they recommend for general cooking, when you don't want too much olive flavour - you could use other oils instead)
1 tsp vanilla extract
150 g cocoa powder
200 g plain flour
2 tsp baking powder

optionally: 250 g of caster sugar (untested, impact on texture and bake time unknown)
245 g raspberries
You will need a liquidiser or food processor to make this like I did.

1. Preheat your oven to 180°C/160°C fan/gas mark 4. Grease 2 sandwich tins with oil or butter. Line them with baking parchment if they don't have removable bases (I simply cut a c. 20 cm wide strip of baking parchment that was long enough to stick out each end and put it across the middle of the tin - it's the lazy way to line sandwich tins, but doesn't give such perfect results as cutting the paper to fit perfectly).
2. Put your (cooled) boiled beetroot and the oil in your liquidiser or food processor and then crack in the eggs and add in the vanilla. Liquidise/food process them until you have a smooth pink liquid To do this without a food processor, grate the beetroot and then stir/whisk the aforementioned ingredients by hand (this will change the finished texture).

3. Sift the cocoa powder, flour, and baking powder together into a large bowl. (If you were going to add sugar, now would be the time.) Mix the dry ingredients, then make a well in their centre.

4. Pour the pink liquid into the well in the dry ingredients.

5. Mix together. I used a spatula and the resulting mixture was quite dry.

6. Roughly chop the raspberries.

7. Add these to the cake mixture and stir well. This will make the mixture much wetter and will largely break up the raspberries and leave the raspberries distributed within the mixture to different degrees, so you run into occasional pockets of intense raspberry in the finished cake.

8. Divide the mixture between your two sandwich tins and smooth down with a spoon or spatula so that the surface is level.

9. Bake in the oven for around 25 minutes. If you insert a skewer into the cake it should come out clean when the cake's done. Also, when the cake's done, if you push its surface down a little, it should rise back up when you let go.

10. Turn out to cool on a cake rack.

11. You now have options about how to serve it. 

I served individual slices from a single sandwich layer, like a fancy chocolate torte from a restaurant. 

If you have no issues about eating sugar or similar substances and you didn't already add sugar, I recommend drizzling maple syrup all over it. This solves all of the problems about it not being sweet enough, but completely takes away the point of not adding sugar. 

Alternatively, you could serve it with single or double cream.

Or you could put the two layers one on top of the other with raspberry jam or Philadelphia-style soft cream cheese or Mascarpone or whipped cream (optionally with raspberries) or icing* (for instance chocolate icing, raspberry icing** or icing for red velvet cake) in between and optionally with more icing or cream over the top or over the rest of the cake.
Doing something along the lines of a black forest gateau, but with raspberries instead of cherries might work well.

All of these suggestions except the maple syrup and serving it plain are untested, but they feel like good flavour matches to me.

*Icing is called frosting in US English.

** Confectioner's sugar is US English for icing sugar and you can convert cups to grams here or you can use a measuring jug. One US cup is 236.6 ml.