I have followed the instructions in this video from Delia Smith precisely, twice:  https://www.deliaonline.com/cookery-school/second-term-perfect-eggs/lesson-6-separate-ways-eggs-part-2  What I get from the final product is a custard which is very egg-like is taste. Not overpoweringly so, but enough that it puts people off eating it.  Is this because there are 6 egg yolks or is there an obvious mistake that a newbie like me is likely to make?  Is it simply that 6 egg yolks is too much? Would the custard be a lot thinner and runnier if I reduce it to, say, 3?  The recipe in full:   6 egg yolks 600ml heavy cream 125g caster sugar 1 level table spoon of cornflour 2 teaspoons of vanilla essence   Heat the cream on the lowest setting.  Sieve the cornflour and sugar together.   Mix the egg yolks into the cornflour and sugar until smooth.   Mix the vanilla essence into the egg yolk mixture.   When a single bubble appears on the surface of the cream, indicating the cream is just about simmering, pour the pan of cream slowly into the yolk mixture, whisking constantly.   Once the cream is all mixed in, return to the pan and place back on the same low heat and continue whisking until the desired thickness is achieved.   Put in a dish and serve or cover with cling film and place in the fridge. 
To reiterate a bit what @dlb said, the egg yolk is what provides the thickness and structure to your custard, so if you cut the yolks by half, you will definitely get something thinner. However, while the eggs are obviously the source of the eggy flavor, there are ways to try and remedy that beyond reducing the egg.  The first thing I would try is just adding an extra teaspoon or two of vanilla. Also, since your recipe does not include salt, add a pinch or two of salt (you won't taste it, but it will make the sweet and vanilla flavors stand out a bit more.) Flavor is a balancing act, and it makes sense to start with the smallest changes you can.  Another thing you can try is replacing some of the cream with evaporated milk or sweetened condensed milk. Those both have a very strong milky flavor that could balance out the egginess, but of course that might not seem any better to you or your friends. If you think your custards plenty thick as it is, you could even just add a tablespoon or two directly, instead of fussing with substitutions.  if you are determined to use fewer eggs, however, you could just go in a more pudding direction-- Basically add some more starch/flour to make up for the missing egg yolks. You will get a different texture, so experiment with your ratios. You can also look around at different pudding and custard recipes online just to get an idea of different egg/starch/etc. ratios out there.  Custard and pudding are honestly pretty forgiving mixtures. Even if you completely screw up and lumpify your mixture, put it through a strainer and you've got something. If it's way too liquid? You can use that as an ice cream or French buttercream base. Are all your strainers dirty? Get some flour, yeast, that box of expired raisins from the back of the cabinet, some spices, and bam. You've got a fruit cake you can freeze and give someone for Christmas! (I actually made fruit cake with some custard I had curdled all to heck on an unfamiliar stovetop. But it was February so I just kept it lol.)  