Preheat oven to 400°; pat chicken dry, spread chicken with ranch + season with salt/pep; add chicken to sheet pan, drizzle with 1 tbsp oil + roast 15-20 min until fully cooked, no pinkness remains

Spread broccoli on a second sheet pan; drizzle on 1 tbsp oil + salt/pep + bake 10-12 min or until browned + tender

Meanwhile, peel + cut potatoes into 1-inch pieces; add potatoes + 1 tsp salt to large pot + fill with cold water, covering potatoes by 1-inch; boil 15-20 min til tender; drain + reserve ½ cup of water; mash potatoes with ¼-½ cup reserved water, creamy horseradish + salt/pep til smooth

Divide all to plates—nicely done!