How do you finish a timber desk top?

[#1]

I highly recommend following the advice in the step-by-step guide How to restore wooden furniture. In the video, you'll see how the Bunnings team member sands the table flat using different grit levels of sandpaper.

The trick is to start with a very coarse sandpaper like 40 grit to remove any major imperfections on the top. Then you start going up the grit numbers until you reach a very fine sandpaper like 300 or 400 grit. At this level, you're removing the splinters in the wood and getting a very smooth surface.  
 

The benchtop should be smooth and silky to the touch after sanding it with 400 grit sandpaper.

I then recommend using Cabot's 1L Water Based Matt Cabothane Clear Polyurethane Varnish. Apply the varnish with a high-quality brush. Many projects have I seen ruined because they used a cheap brush. - EricL