Place the 3 tablespoons butter, rosemary, thyme, garlic, salt and pepper in a small bowl and use a fork to mash it into a blended paste. Loosen the skin of the bird carefully, and then rub the butter mixture underneath the skin and over the skin, trying to spread it as evenly as possible.
If you want a crisper skin, Turn the instant pot to Sauté and brown the turkey breast skin side down, first tilting it so the skin browns on one side of the breast, then the other, for about 2 minutes per side, so that most of the skin is at least a bit browned. Remove the turkey breast, and add the onions and celery, and sauté or 3 minutes until softened and golden. Turn off the Instant Pot, add the broth then place the turkey breast into the pot skin side up. If you have a removable rack, such as this one, insert that into the Instant Pot before adding the turkey breast.
Close the lid and set the vent knob to sealed. Set the instant Pot on High Pressure, for 25 minutes. Once the cooking time has finished, allow the pressure to release naturally for 10 minutes, then open the valve to release any remaining pressure. An internal thermometer inserted into the middle of the breast should read 160°F (the temperature will climb another 5 degrees to a safe internal temperature of 165F while it is resting). Remove the turkey breast and place it on a cutting board with a little moat to catch any juices and tent with foil. Let rest for 15 minutes before slicing.
If you want the skin to be more browned and crispy you can preheat the broiler, and then place the turkey breast skin side up in a baking pan and broil it for a few minutes, watching carefully so that it doesn’t burn.
Meanwhile, make the gravy: Strain the cooking liquid and discard the solids. Return the inner pot back into the Instant Pot, and set it to Sauté. Add the 2 tablespoons butter and when it is melted add the flour and whisk until it is light brown; this is called a roux and it will thicken the gravy. Add ¾ cup of the strained cooking liquid to the pot while whisking. Continue whisking for another 2 or three minutes until the gravy is simmering and starts to thicken. Taste and add salt and pepper as needed.