For the Watercress Purée:
Blanch and shock watercress. Squeeze out the excess water and blend the watercress with the cold water. Strain, then season with salt.
For the Smoked Date Purée:
Blanch and drain the pitted dates. Press the dates through a tamis and place the purée in a small pot. Slowly mix the soft butter into the dates. Cold-smoke the mixture for 5 minutes, then season with salt.
For the Garlic Emulsion:
Place the olive oil in a saucepan. Cut the heads of garlic in half horizontally and place cut sides down in the saucepan. Once garlic is golden in color, add the milk, bring to a simmer and steep for 30 minutes. Strain and season with salt.
To Assemble and Serve:
Blanch and shock the pearl onions; then and halve them. Sear in a hot pan to caramelize the edges. Roast the boudin blanc slowly, season and cut into smaller pieces. Brush the milk skins with cream and warm up gently. Plate the boudin blanc with the date and watercress purées, garlic emulsion and pork jus. Garnish with the pearl onions and watercress sprigs.