Poke russet potatoes all over with a fork. Bake until potatoes are easily pierced with a fork (around 60-70 minutes). Once done, set the potatoes aside to cool and leave oven on.
While that potatoes are in the oven, add olive oil to a large skillet on medium-high heat. Break the beef up and add it to the pan.
While cooking, sprinkle with sea salt, pepper, and garlic powder.
Right before the beef is done, turn heat to medium, and throw in the minced onion, celery, and carrot.
Let everything cook until it's done all the way through then add Worcestershire sauce. Again, the amount is up to you as I taste as I cook and adjust accordingly.
Set aside once it is done.
Moving on back to the potatoes, once they're done and cooled off, slice off the top 1/3 to 1/4 of the potato.
Hollow out the potato, but don't forget to leave a "wall" on the insides.
Place the hollowed out bits into a large bowl with your milk and butter.
Using a masher, mash until the it is smooth.
Place the filling inside the hollowed out potatoes before covering the top with the mashed potatoes.
Place the stuffed potatoes back into the oven and let it cook until the peaks of the mashed potatoes are a pretty golden brown.
Let cool and serve
Notes
You can easily substitute the lean beef with lamb for Shepherd's Pie!