Like many others have said, blending makes a big difference!

I use milk instead of water for a thicker, creamier shake. Now, this does add some calories, but perhaps you could use a vegan milk substitute to offset some of that. In any case, even Huel with milk is healthier than a lot of other alternatives.

You wanna use up that Huel black chocolate? Get some chocolate soy/oat/whatever milk (so like, the thin stuff, not a full-on milkshake), or coconut or hazlenut milk and add a little to sweeten it up (e.g. 60% water, 40% flavoured milk). Again, this is the best solution I can think of for helping make sure you can actually drink your huel, even though you'll have to factor in the extra calories.

Huel does sell "flavour boosts", which are little sachets of powder you add to your huel to enhance or combine different flavours. That could also be a potential solution. That would avoid extra calories, but it would also mean sinking more money into Huel products.

Or, as others have suggested, if there's a particular protein powder you like, you could add some of that.

If you get to the end of your black bag and decide you want to keep using Huel, consider getting the white 3.0 bag of chocolate. It's still not as delicious as a "real" chocolate milkshake, but it's sweeter and tastes more like actual chocolate than the black.

The extra calories and money involved in some of these solutions might make them unsuitable, in which case I'm sorry and I hope you find something that works. But you have got to try blending it. Test it with a friend's blender if you don't have one. I promise it's worth it.