In a small bowl, whisk together the honey, vinegar, Dijon mustard, whole grain mustard, and olive oil.
Season the chicken with salt and pepper. Place in a large zipper lock or vacuum seal bag with the mustard sauce. Seal the bag using the water immersion technique or vacuum sealer on the moist setting.
Place the bag in the water bath
When the timer goes off, remove the bag from the water bath. Remove the chicken from the bag and pat dry with paper towels. Reserve the cooking liquid in the bag.
Melt the butter in a medium skillet over medium-high heat. When the butter stops foaming, add the chicken and sear until golden brown, about 20 seconds per side. Transfer to a cutting board and let rest for 5 minutes.
Return the skillet to medium-high heat and add the reserved cooking liquid. Bring to a rapid simmer and reduce just until it begins to change color, 10 to 30 seconds. Remove from the heat