Put the oils in a jug with the garlic clove and leave for 15 minutes or so to infuse. Fish out the garlic clove and throw it away.
In a small processor, or with a hand-held blender, whiz the eggs until they become very thick. Add the mustard, vinegar, lemon juice and ½ teaspoon of salt and whiz together. With the motor running, add the oil drop by drop and continue mixing until all the oil has been added and the mixture is thick and fluffy. Taste for salt and pepper. Cover the bowl and keep in the fridge. This is nice after it has been chilled for a couple of hours and it keeps for a few days in the fridge if well covered.