In a very large skillet, over medium heat, add the olive oil, butter and onions.
Cook the onion for just 2 – 3 minutes.
Add the garlic; cook for 2 more minutes.
Next, add the sweet potato and the russet potato; sweet potato will cook a little faster than the russets, but it’s okay to add them both at the same time when preparing a hash recipe.
Add the salt and ground black pepper; toss to combine.
Add 1/2 cup of the water and continue to cook for 20 minutes; stirring occasionally.
Add the remaining water; stir to combine and distribute; cook for another 20 minutes.
Taste to see if the potatoes are fork tender and turning into a mash/hash.
Add the thyme leaves, parsley, and nutmeg; stir to combine; taste for seasoning and adjust if needed.
Remove from heat and serve.