Preheat oven to 450 degrees F. Lightly oil a baking sheet or coat with nonstick spray.
Place cauliflower in a single layer onto the prepared baking sheet. Add olive oil; season with salt and pepper, to taste. Gently toss to combine.
Place into oven and bake for 20-25 minutes, or until golden brown.
Using paper towels, pat both sides of the chicken dry; season with 3/4 teaspoon salt and 1/2 teaspoon pepper.
Melt butter in a Dutch oven over medium heat. Working in batches, add chicken, skin-side down, and sear both sides until golden brown, about 2-3 minutes per side; set aside. Drain excess fat, reserving 2 tablespoons in the Dutch oven.
Add shallot, and cook, stirring occasionally, until tender, about 3-5 minutes. Stir in garlic and thyme until fragrant, about 1 minute.
Whisk in flour until lightly browned, about 1 minute.
Stir in chicken broth and wine, scraping any browned bits from the bottom of the Dutch oven. Return chicken to the Dutch oven.
Bring to a boil; reduce heat and simmer, covered, until chicken has completely cooked through, reaching an internal temperature of 165 degrees F, about 15-20 minutes. Remove chicken and keep warm.
Stir in spinach, Parmesan and half and half until the spinach has wilted, about 3 minutes. Stir in cauliflower until heated through, about 1-2 minutes. Return chicken to the Dutch oven.
Serve immediately.
Notes
Cut cauliflower into similar-sized pieces. Dice the cauliflower florets into similar bite-sized pieces to ensure even cooking.
Skip lining the baking sheet. Lining a baking sheet with parchment paper or aluminum foil makes for easier clean up, but this will also serve as a physical barrier. Skip lining the baking sheet for deeply browned, crispy, caramelized edges on the cauliflower florets.
Use a heavy pot. A heavy bottom pot, such as a Dutch oven, is ideal here for even heat distribution.
Use bone-in, skin-on chicken thighs. The skin crisps up perfectly in this recipe, and the bone-in allows for deeper, meatier flavors.
Cook in batches. An overcrowded pan can lead to uneven cooking and poor browning. Work in batches to maintain high heat for a good sear and a golden brown crust on each chicken thigh, yielding juicier, tender meat.
Choose a wine you will drink. A dry white wine (pinot grigio or sauvignon blanc) is great here – it does not have to be anything fancy or overpriced. Just something you don’t mind sipping on since you will have an open bottle.
Swap the wine for broth. Substitute chicken broth for white wine as a non-alcoholic substitute.
Deglaze the pan. Deglaze the Dutch oven with chicken broth and wine (if using), lifting up all the browned bits from the bottom of the pan to capture maximum flavor and to build a rich pan sauce for the chicken and cauliflower.
Choose your dairy. Heavy cream will yield a richer cream sauce whereas whole milk will yield a lighter, thinner sauce. Half-and-half is ideal for a mild, creamy consistency.
Use an instant-read thermometer for the most accurate results. The internal temperature should reach 165°F.
Reheat in the oven. Leftover chicken can be rubbery when reheated. For best results with leftovers, reheat in the oven at 350°F, covered in aluminum foil, until warmed through.