Blanch broccolini in salted water for 45-60 seconds.
Drain and set aside.
Season chicken breasts with black pepper and old bay seasoning.
Dredge it in tapioca flour.
Heat pan on medium high heat with olive oil.
Sear chicken until golden brown, about 4 minutes each side, and set aside.
In the same pan, saute shallot until soft, then add garlic to cook for 30 seconds.
Pour in white wine to de-glaze pan, scraping up all the brown bits at the bottom of the pan.
Add in chicken stock and bring to boil, then add mustard and thyme.
Pour in cream, and bring to a simmer, and lower heat.
Allow to simmer for 5 minutes, season with salt and black pepper, then stir in slurry to thicken sauce.
Add chicken back into the pan, cover, and simmer on low heat for 5 minutes.
Remove from heat, and top with blanched broccolini.
Cover and let it sit for 5 minutes before serving. This will help reheat the broccolini.