1. Combine cauliflower and potatoes in a large saucepan and add enough water to cover by 1/2"; season generously with salt. Bring to a boil and cook until vegetables are very tender, about 10 minutes, then drain and return to saucepan. Mash until smooth, then stir in 4 tablespoons butter and season with salt and pepper to taste; set aside.
2. Melt remaining 2 tablespoons butter in a large broiler-safe skillet over medium-high. Add mushrooms, carrots, and onion, season with salt and pepper, and cook until vegetables are soft, 7 to 9 minutes. Add garlic and tomato paste and cook, stirring constantly, 30 seconds, then stir in flour until fully incorporated. Add turkey and cook, stirring to break up meat, about 1 minute.
3. Stir in broth, Worcestershire sauce, and thyme, scraping up any browned bits on bottom of skillet. Bring to a simmer and cook, stirring occasionally, until liquid is slightly thickened and turkey is cooked through, about 3 minutes. Stir in peas, remove from heat, and season with salt and pepper to taste. Smooth top of filling into an even layer.
4. Place a rack in upper-middle of oven and heat broiler. Dollop potato mixture evenly over filling and smooth into an even layer with a rubber spatula; if desired, gently drag the tines of a fork across surface to make decorative ridges. Broil until topping is golden brown, 5 to 10 minutes. Let sit 10 minutes before serving (skillet handle will still be very hot).
Source: Hannaford fresh Magazine, January-February 2021