The night before:
Cook the diced bacon in a heavy skillet or cast iron skillet until crisp. Remove the bacon pieces with a slotted spoon to a paper-towel lined plate to cool.
Reserve 2 tablespoons of the bacon fat. Reduce the heat to medium and add the onion and celery until tender. Add the minced garlic and cook 1 minute, then remove from heat.
Add the chicken stock to the slow cooker and add the salt, white pepper, dry mustard, dried tarragon, and garlic powder. Whisk to combine. Add the potatoes.
Store the soup mixture, covered, and the bacon pieces in an airtight bag or container in the refrigerator.
On cooking day:
Remove the soup mixture from the refrigerator and set the slow cooker on low. Cook for 6-8 hours.
Before serving, uses an immersion blender to pulse the mixture, leaving some pieces of potato intact. Stir in the heavy cream and half the Gryuere cheese.
Serve with crispy bacon pieces and additional cheese, as desired.