Cook the peppercorns in a small skillet over medium, stirring occasionally, until fragrant and lightly toasted, 3 to 4 minutes. Remove from heat, and cool completely, about 5 minutes.
Crush the toasted peppercorns. Whisk together extra-virgin olive oil, orange juice, lemon juice, tarragon, mustard, pinch of kosher salt, and crushed peppercorns in a medium bowl. Use immediately, or refrigerate in an airtight container up to 2 weeks.
