The technique uses Charles' Law from gas physics.
Preheat your oven to no more than 325F. Slather the spoon (whatever) with the food grade oil of your choice. I use olive oil.
Now, on a cake rack over a sheet pan, into the oven for no more than 3 mins 30 sec by the clock.
What's happening:
The heat causes the wood air to expand (Charles' Law).
Out of the oven to cool, the reverse happens, the remaining wood air contracts and sucks the oil into the wood.
This means that you can't wash it off, you can't get the oil to move unless you reheat to 325+.
In hot soup, wood air expands to push off any room temp oil finish and as the spoon cools, soup is sucked into the wood.
May explain why lots of really old wooden spoons are black like the bottom of a compost bin.
Further, claims will be made that the oil finish will go rancid. Hardly likely as there's now so little air in the surface wood.
There's always the risk that this heating process will crack the wood. I carved and baked 70 spoons and 30 forks with no problems.