In a medium sized saucepan, melt the butter over medium heat. Add the onion and cook until translucent, about 2-3 minutes.
Add in the flour and coat the onion to make a roux. Pour in the chicken broth, whisking continually until it comes to a simmer. Remove from heat.
Pour the chicken broth mixture into the crockpot, then add the potatoes, thyme, salt and pepper. Cover and cook on low for 6-7 hours or on high for 4-5 hours.
When the potatoes are tender add the bacon, heavy cream, sour cream and cheddar cheese then cover and cook on high for an additional 20 minutes.
When ready to serve, turn off the heat and sprinkle with green onions.
Don’t skip the roux: Starting with a butter-flour mixture prevents the soup from being watery and gives it a velvety texture.
Dice potatoes evenly: This ensures they cook at the same rate and break down properly for a creamy consistency.
Use freshly shredded cheese: It melts more smoothly than pre-shredded and avoids a grainy texture.
Adjust thickness if needed: For a thinner soup, add a splash of broth or milk after cooking. For thicker, mash some of the potatoes directly in the crockpot.
Wait to add dairy: Stir in cream, sour cream, and cheese at the end to avoid curdling.
Taste before serving: Depending on your broth and bacon, you may not need additional salt.