Add the olive oil and buckwheat flour to a pan with a heavy base
Cook for 5 minutes over a low heat, stirring regularly, to make your roux
Don't allow the roux to colour
When ready, the roux will have a slightly sandy texture
Add the warm poaching liqueur bit by bit to the roux (roughly 1/4 of a cup at a time)
To prevent lumps in your veloute, thoroughly mix each addition of liqueur into the roux with a wooden spoon before adding more
Initially, the roux will swell and appear to form a heavy dough-like mix. As you continue to add liqueur it will eventually loosen and form a thick sauce
Season with salt and pepper to taste
Strain your veloute for lumps, just in case :-)