Preheat the oven at 160 degrees Celsius.
Remove the stalks of the beetroot, leave them unpeeled, wash them under cold water and dry them in a towel (it is better if you use paper towels).
Slice the beetroot as thinly as possible with a mandoline or a very sharp knife. Place the slices in a bowl, add the olive oil (just a few drops) and use your hands to evenly distribute the oil on every slice. Every slice should be covered in a very thin coat of oil.
Line an oven tray with baking paper and place the beetroot slices on the baking paper, one next to the oder (do not put all slices at once as they will not bake evenly and they will not become crispy).
Bake the beetroot slices at 160 degrees Celsius for 20-25 minutes (depending of how thin they are), check them after 20 minutes, just to make sure they will not burn. You will know that they are ready, when they start to shrink and become crispy.
When ready, take the crisps out of the oven, sprinkle some coarse sea salt, leave them to cool and then add some fresh thyme.