Heat the Instant Pot using the Sauté function and add the butter.: You will hear a gentle hiss as the butter melts and begin to smell a faint toasted dairy note, which signals the pan is ready. This warm, glossy fat creates the base that helps the aromatics release their flavors. If the butter begins to brown too quickly and smell nutty, reduce the heat or cancel the sauté briefly, because burnt butter will add bitterness. Make sure the inner pot shows a shimmering surface without smoking before you add vegetables.
Once the butter has melted, add the carrots, celery, onion, and mushrooms to the pot and stir to coat all of the vegetables with butter.: At this stage you should see a glossy sheen on the vegetables as the butter clings to their surfaces. Stirring helps distribute heat and start the softening process evenly. The garlic and sage are withheld until later to preserve their aromatic qualities. If the pot seems dry or the vegetables stick, add a splash of stock or a touch more butter , because sticking can lead to burnt bits that will make the broth taste acrid.
Cook for 5 minutes, or until the vegetables are tender and starting to brown.: Listen for soft sizzling and watch for edges of the onion and carrots to take on a light golden color; this is where flavor concentration develops through gentle caramelization. The kitchen will start smelling sweeter and more complex. If some pieces are browning much faster than others, stir and redistribute them, because uneven browning creates inconsistent flavors in the finished soup.
Next, add the garlic and sage and cook for an additional minute.: When you add the minced garlic and fresh sage , you should immediately notice a bright, herbaceous aroma that becomes more pronounced as the oils are released. This brief heat time is just enough to bloom their aromatics without turning the garlic bitter. Avoid leaving them in the hot pot unattended, because overcooked garlic will develop a harsh, acrid flavor.
Add the chicken stock, turkey, noodles, salt, pepper, and bay leaf and stir to combine.: As the hot chicken stock hits the sautéed vegetables, steam will rise and the room will fill with savory notes. Stirring helps distribute the shredded turkey and dry noodles , so nothing clumps together when pressure builds. Ensure the noodles are submerged for even cooking. If the pot seems overfull or the liquid does not cover everything, remove some solids or add a bit more stock, because insufficient liquid can prevent the Instant Pot from reaching pressure.
Attach the lid and ensure the valve is in the sealing position. Set the Instant Pot to Pressure Cook – Manual for 3 minutes.: You will hear the mechanism click as the lid locks, and the pot will hiss quietly while it comes to pressure. Once the timer runs, the noodles will have a soft, tender texture that absorbs the broth. Using a brief pressure cycle keeps the noodles from becoming mushy while ensuring the flavors meld. If the pot takes unusually long to reach pressure, check that the gasket is seated correctly and that the valve is set to sealing, because steam leaks will prevent proper cooking.
Once the Instant Pot has finished cooking, release the pressure manually by switching the valve to the venting position. Be careful, it may spit and steam when the valve is opened!: You will experience a loud rush of steam and a burst of fragrant broth aromas; stand back and use a long utensil to move the valve to venting. This quick release stops the noodles from continuing to soften. If the venting spits aggressively, pause and allow a few seconds between adjustments, because too rapid a release can splatter hot liquid.
Remove the bay leaf and adjust the salt and pepper as needed. Serve warm.: After the steam settles, fish out the dried bay leaf and taste the soup, noting how the flavors have concentrated. Adjust the kosher salt and ground black pepper a little at a time until it sings. Serve in warmed bowls so the soup stays hot longer. If the broth tastes flat, a small pinch more salt will usually brighten it, but add incrementally so you do not over-salt.
Store any leftover soup in an airtight container in the fridge for up to three days.: As the soup cools, the noodles will continue to absorb broth, softening further. For best leftover texture, store in a sealed container and consider refrigerating the soup without the noodles if you plan to freeze, because freezing can make the noodles mushy. Reheat gently on the stove or in the microwave, stirring to redistribute heat evenly.