I've done the following recipe, intending to push it up to 18 or more %, but we had a little taste recently and it's strong enough and tastes not unlike Tia Maria so when the yeast finally gives up, or possibly just later this week, I'm going to bottle it - it'll be standard wine strength, I think - maybe a little more..
2lb sugar dissolved in warmed water, 4Tbsp instant coffee added, cooled a bit while yeast rehydrates, into demi with 1tsp citric, 1tsp nutrient - plenty of headspace left for later feeding. Pitched yeast (Gervin D)
After 5 days, added 1/2lb sugar dissolved in 1/2l warmed water
After 10 more days, added another 1/2lb sugar dissolved in warmed water
After another week, added 1/4lb sugar dissolved in 1/4l warmed water
After a further month, removed a 250ml sample and added 4oz sugar in 250ml water.
With a yeast that can handle the sugar concentration, you could probably just stick it all in at the start. I probably could have with Gervin D.
It's still pretty sweet but a very interesting flavour. I'm going to bottle it in 275ml J2O bottles, as I suspect it's the kind of thing you only want one glass each of, at the end of the evening.
Your missing ingredient may have been vanilla?
Cheap wine for christmas... If you can get frozen or tinned strawberries at a sensible price, it's my fave right now. They just need a bit of acid (I used citric) and some tannin (I used tea). And of course nutrient for the yeast.