For the Pork Tenderloin with Roasted Grapes: Preheat the oven to 375 degrees F.
Cook the bacon lardon in a large skillet over medium heat until crisp, 5 to 6 minutes. Use a slotted spoon to remove the bacon and drain on a towel-lined plate. Reserve the bacon for the potatoes. Reserve the skillet with bacon fat to cook the pork.
Toast the fennel seeds in a small skillet over medium heat until fragrant, about 2 to 3 minutes. Transfer to a spice grinder and grind into a fine powder.
Season the pork generously with salt and pepper. Return the large skillet with bacon fat to medium-high heat. Place the pork in the pan and cook on all sides until rich golden brown, about 8 minutes. Remove the pork from the pan, dust the pork with the toasted ground fennel seeds, and place on a sheet pan fitted with a rack. Roast in the oven until the internal temperature reaches 150 degrees F, about 14 minutes. Allow to rest 10 minutes until ready to serve.
Drain the fat from the skillet and place over medium-low heat. Add the extra-virgin olive oil and shallots and cook until softened, about 2 minutes. Season with salt then pour in the port and scrape with a wooden spoon to release the bits from the bottom of the pan. Add the grapes and cook the grapes until they split and let out their juices, about 10 minutes.
Add half of the chicken stock, let it reduce slightly, then add the remaining stock and let cook until sauce is reduced by half and thickened, 8 to 10 minutes. Taste and re-season if needed.
For the Mashed Sweet Potatoes: Add the sweet potatoes to a large pot and cover with cool water. Bring to a boil and cook until tender, about 15 minutes. Drain and return the cooked potatoes to the pot.
Add the heavy cream and butter and combine with a hand mixer until smooth. Mash with a potato masher. Add the brown sugar, heavy cream and cumin and mix with a spatula to combine. Season to taste with salt. Add the cayenne, cumin, light brown sugar, reserved bacon and some salt and fold to combine.
Slice the pork on a bias. Serve with the sweet potatoes and top with the grapes, sauce and chives.