Hi. Quite new to composites, dabbled about a bit done lots of research online and bought some books, but after a couple failed moulding attempts I've decided to try a simpler project and reach out for help! 
Front winglets seem to me a simple project to make.
 looking at making a pair similar to what's in the picture. I could get my hands on a pair of ali ones to take a mould from. I plan on taking moulds using the Uni mould kit. Need advice on how to get both sides cosmeticly pleasing. Mould of each face and bond together with foam core? Split mould designed to be a closed mould and used to compress the CF producing one piece straight from the mould? Just need advice on this before I start making the mould as would affect the design.

Many thanks

If the surfaces are flat I would do as Warren suggests. Make a sturdy mould of one side only and place a polished folded aluminium plate (treated with several layers of release agent) on the other side. Plate needs to be 4mm thick in order to prevent vacuum pressures distorting it. However, bending plate this thick may result in cracks along the outside of the bend and these will need to be sanded/filled. If you can't bend 4mm you will probably get away with using 3mm or even 2mm. on a small/thin item such as this.

Update. Rethinking this, you could possibly make both sides of the mould out of 4mm aluminium. The only issue I can think of is the possibility of vacuum distortion but, with a total of 8mm thickness of aluminium this is unlikely IMO. The mould would be quick, cheap and easy to make. I recently made these aero deflectors (still to be cut to shape) out of 4 layers of 375gm prepreg carbon laid on both sides of a 1.5mm thick aluminium mould (thereby making a pair using one mould :-) ). 120 dec C curing and no distortion.

I wouldn't bother with a core, just use more layers of carbon (6 layers of 2-300gm will be ample, probably get away with 4 with such a narrow piece.). Using a core means that you have to deal with the exposed edges (unless you can wrap the carbon around them which isn't easy). Using only carbon does away with this.