Wash the peppers and prick several times with a knife. Peel the shallots and cut into slices. Simmer vinegar, mustard seeds, bay leaf, sugar, peppercorns, salt, shallots and 1/4 litre water for about 10 minutes.
Layer/fill the peppers in 2 clean glasses. Pour in liquid evenly (pods must be covered) and close immediately. Leave the peppers to stand in a cool, dark place for approx. 4 weeks.