Place prepped potatoes and chicken broth in a 4-6 quart pot. Bring to a boil over medium high heat. Cover. Reduce heat and simmer until fork tender, about 10 minutes. Drain potatoes in colander placed over a large bowl to reserve the broth. Set aside.

Return pot to stove over medium heat. Add butter. When melted add onion and sautée about 2 minutes. Wisk in flour and cook 2 minutes more.

Carefully add broth back to pot, wisking constantly to prevent and break up any lumps. As soon as broth is smooth and begins to thicken wisk in half and half, and then milk.

Increase heat to medium-high. Bring to a simmer until about the thickness of a loose gravy, wisking constantly. This took about 5 minutes from adding the milk to thickened for me.

Wisk in salt amd pepper (and celery seed if using). Taste and adjust seasoning as desired. Carefully return potatoes to pot. Gently stir with a wooden spoon to incorporate. Serve immediately. Enjoy!