1. Pat chicken thighs dry. Lay them skin-side down on a cutting board. Use a meat mallet to gently flatten them to an even thickness (about 1/2 inch) without tearing. Season lightly with salt and pepper.

2. In a skillet, heat olive oil over medium heat. Add chorizo and cook until lightly crispy and fat is rendered. Remove chorizo and set aside. In the same skillet, add minced garlic and cook for 30 seconds until fragrant.

3. Add chopped spinach to the skillet and cook until wilted. Squeeze out any excess liquid. Combine the cooked spinach, chorizo, cooked squid, chopped parsley, and smoked paprika in a bowl. Mix well and season with salt and pepper.

4. Lay a piece of plastic wrap or parchment paper on your work surface. Place a flattened chicken thigh on it. Spoon a portion of the filling onto the wider end of the chicken. Carefully roll the chicken tightly around the filling to form a cylinder. Twist the ends of the plastic wrap tightly to secure the ballotine's shape.

5. Repeat with remaining chicken thighs and filling. Vacuum seal each ballotine in a separate bag. If you don't have a vacuum sealer, use the water displacement method with a zip-top bag.

6. Preheat your sous vide water bath to 60°C (140°F). Carefully place the sealed ballotines into the water bath and cook for 1 hour 45 minutes (105 minutes).

7. Once cooked, remove the ballotines from the water bath and immediately plunge them into an ice bath for 10 minutes to stop the cooking process and chill slightly, or pat dry if serving immediately.

8. To serve, remove the ballotines from the bags. Heat butter in a skillet over medium-high heat until shimmering. Sear each ballotine for 2-3 minutes per side until the skin is golden brown and crispy. Slice into thick rounds and serve immediately.