1/3 cup Colman’s dry mustard
1/2 cup white wine vinegar
1 tablespoon minced canned chipotle chile in adobo, plus 2 tbsp. adobo sauce from can, divided
1 large egg
1/2 teaspoon salt
2 teaspoons cornstarch
Stir together dry mustard, vinegar, and 1/4 cup water in a medium metal bowl until smooth. Stir in minced chipotle chile (leave sauce behind). Chill, covered, overnight.
Bring a medium saucepan filled with 1 inch of water to a simmer. To bowl of mustard mixture, add egg, salt, and cornstarch and whisk to blend. Set bowl over simmering water and cook, whisking constantly, until just thickened, 3 to 5 minutes. Stir in adobo sauce.
Make ahead: 2 weeks, covered and chilled.