Season the turkey breast with salt and pepper and place in a large zip-lock bag. Seal using the water immersion technique, set the Anova Sous Vide Precision Cooker to 145F (62C), place the bag in the water bath and set the timer for 3 hours.
Meanwhile, set a large skillet over medium-high heat and add the oil and butter. When the butter foams, add the onions and mushrooms and cook until they start turning golden, about 5 minutes.
Shake the flour overtop and stir to coat. Add the stock and cream, bring to a simmer and cook until the sauce has thickened. Remove the cooked turkey breast from the sous vide bag, slice and slide into the pan with the sauce, or serve with the sauce spooned overtop. Serves about 4.