Carefully remove the skin from the chicken thigh, keeping it as intact as possible. Cut the beef belly into small, uniform lardons (approx. 1/4 inch cubes).

Place the chicken skin, fat-side down, in a cold non-stick skillet. Turn heat to medium-low. Slowly render the fat for 10-12 minutes until the skin is golden brown and perfectly crisp. Remove to a paper towel-lined plate to drain and cool. This slow rendering is crucial for crispness.

In a separate small saucepan, melt the butter over very low heat. Add the boneless chicken thigh to the melted butter, ensuring it's mostly submerged. Poach gently for 8-10 minutes, maintaining a temperature just below a simmer (around 80-90°C / 175-195°F). The chicken should be incredibly tender and juicy. Use a meat thermometer to ensure an internal temperature of 74°C (165°F).

While chicken poaches, add the beef lardons to the skillet used for the chicken skin (no need to clean, residual fat is good). Cook over medium heat for 5-7 minutes, stirring occasionally, until deeply golden and crisp. Remove lardons to a paper towel-lined plate.

Carefully remove the poached chicken thigh from the butter. Slice or shred as desired. Arrange the chicken on a serving plate. Crumble the crispy chicken skin over the chicken and scatter the beef lardons alongside. Drizzle with some of the flavorful poaching butter. Serve immediately.