Combine melted butter, maple syrup, dijon mustard, garlic powder, and sea salt.
Place the turkey breast in a large tupperware and pour butter mixture over turkey, rubbing under the skin and on both sides.
Cover and refrigerate at least 4 hours, up to overnight.
Once ready to cook, stuff onion and celery stalks (as much as you can) into the turkey breast cavity. If you can't fit it all, just place it on the bottom of the Instant Pot/around the turkey breast.
Place trivet in Instant Pot.
Add chicken broth to Instant Pot.
Place turkey onto trivet, along with any onion/celery that didn't fit inside of the turkey breast.
Place lid on Instant Pot, making sure it is sealed.
Cook on high for 35 minutes, and let pressure naturally release for 15 minutes.
Preheat oven to 425.
Place turkey breast onto baking sheet and bake in oven for 10 minutes, until skin is browned.
While turkey is in oven, make the gravy.
Strain out the celery and onion.
With turkey drippings/liquid still in the Instant Pot, turn the Instant Pot to saute setting.
Add butter and melt.
Whisking vigorously, slowly add the flour. You don't want it to be clumpy so be sure to add slowly and to whisk the entire time.
Let it cook for 1 minute.
Slowly add the cream and dijon, whisking constantly. Let cook until thickened, about 3-5 more minutes. Season with salt and pepper, to taste.
Slice turkey breast and serve with gravy.