01Cut about 30g of butter into small cubes, then place them in the refrigerator to cool.
02In a small saucepan, bring the carrot juice to a boil, then reduce over medium-high heat for about 10 to 12 minutes, until reduced by half.
03Reduce the heat to maintain a gentle simmer, then add the cold butter cubes one by one, whisking constantly and ensuring each cube is fully incorporated before adding the next.
04Once the butter is melted and emulsified, add the clementine juice, then season with a good pinch of salt and a twist of pepper. Remove from the heat.
05Transfer to a small sauceboat-type container and serve immediately with steamed fish, vegetables or potatoes, as desired.