Whisk the sugar, sage, thyme, rosemary, garlic, 5 teaspoons salt and 1/2 teaspoon pepper in a small bowl until combined.
Starting on the top edge of one turkey breast, gently lift the skin to separate it from the meat, but leave a 1/2-inch border around the perimeter where it's still attached to the breast. (You want to make a pocket to hold all the herbs and seasonings.) Stuff half of the herb mixture underneath the skin, massaging it into the flesh and evenly distributing it over the surface of the meat. Repeat with the remaining turkey breast and herb mixture. Let sit uncovered at room temperature for at least 1 hour or wrapped tightly in plastic and chilled for up to 3 days.
Melt 6 tablespoons butter in a 6- or 8-quart Instant Pot® set to the high saute setting (see Cook's Note). Add the flour and cook, stirring constantly, until the roux is deep golden brown and smells nutty, 4 to 6 minutes; scrape into a heatproof bowl and set aside (the roux will continue to darken as it sits).
Add the remaining tablespoon butter and, working one breast at a time, cook skin-side down, undisturbed, until deep golden brown, 6 to 8 minutes; transfer to a baking sheet. Repeat with the remaining breast. Add the wine to the pot to deglaze, scraping up any browned bits from the bottom, and cook until you can't smell alcohol and the wine smells fruity and sweet, 3 to 4 minutes. Add the stock, place the rack in the pot and position both breasts on the rack side by side to evenly cook.
Follow the manufacturer's guide for locking the lid and preparing to cook. Set to pressure cook on the high pressure setting for 15 minutes. After the pressure-cook cycle is complete, follow the manufacturer's guide for quick release and wait until the quick-release cycle is complete. Being careful of any remaining steam, unlock and remove the lid.
Transfer the turkey to a baking sheet and let sit uncovered while you make the gravy.
Set the Instant Pot® to the high saute setting and bring the cooking liquid to a boil. Whisk in the roux and cook until the gravy boils and thickens, about 5 minutes. Turn off.
Cut the turkey crosswise into 1/2-inch-thick slices and top with the gravy.
Settings may vary on your Instant Pot® depending on the model. Please refer to the manufacturer's guide.
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