- 17 tablespoons (2 sticks plus 1 tablespoon) unsalted butter
- 1 large or 2 small oranges, preferably blood oranges
- 1 tablespoon white-wine vinegar
- 1 teaspoon white peppercorns, crushed
- 4 large egg yolks
- Coarse salt
- Juice of 1/2 lemon
Melt butter in a small saucepan over medium heat; slowly bring to a boil, skimming froth from surface. Carefully pour melted butter into a small bowl, holding back the milky sediment in the bottom of the pan. The clarified butter should be the color of light olive oil; let cool to room temperature.
Bring a small pot of water to a boil over high heat; prepare an ice-water bath and set aside. Using a paring knife, remove zest from oranges in large strips, reserving oranges. Add zest to boiling water; cook until softened, about 1 minute. Drain and transfer to ice-water bath to cool. Drain and very finely chop; set aside.
Squeeze juice from oranges into a small saucepan. Place saucepan over low heat and cook until juice is reduced by one third. Add zest to saucepan and remove from heat; set aside to cool.
In a medium heavy-bottomed saucepan, mix vinegar with 1/4 cup cold water and crushed peppercorns. Place over medium-high heat until liquid is reduced by one third; remove from heat and let cool completely. Add egg yolks to cooled reduction and whisk to combine.
Place saucepan on a heat diffuser over very low heat; whisk, making sure the whisk comes in contact with the bottom of the pan. Gradually increase heat, whisking so the sauce emulsifies progressively and becomes smooth and creamy, 8 to 10 minutes; do not let the temperature of the sauce rise above 150 degrees.
Remove saucepan from heat and whisk in clarified butter in a slow, steady stream; season with salt. Stir in lemon and orange juice mixture. Line a chinois or fine-mesh strainer with cheesecloth; strain mixture and discard solids. Use sauce immediately.