For the glaze, melt together butter, sugar and maple syrup ina small saucepan set over medium heat, stirring occasionally.
Once the sugar has melted, add the bourbon, BBQ sauce, apple cider vinegar and hot sauce. Bring to a simmer, then reduce heat to medium-low and leave to simmer until glaze has thickened and bubbles look syrupy. Remove from heat and set aside until needed. (Glaze can be made while chicken is roasting)
For the stuffing, toss together breadcrumbs, lemon zest and juice, salt, pepper, and sage in a large bowl. Set aside.
Melt the butter in a medium sized saucepan set over medium-low heat. Add the onion and sauté gently until onions are soft and translucent.
Add the diced apple and cook for further 1 minute.
Pour saucepan contents over the breadcrumb mixture and toss very well.
Spoon stuffing into a baking dish, set aside. (Stuffing can be made while the chicken is cooking.)
For the chicken, preheat oven to 200°C / 180°C fan assisted.
Place spatchcock chicken in a large roasting tin. Drizzle over olive oil then season well with salt and pepper.
Roast chicken for 40 minutes, then remove from the oven and brush half of the glaze over the chicken. Return chicken to the oven along with the stuffing.
Roast for further 20 minutes, brushing the chicken with the remaining glaze. Finish roasting for a final 10 minutes.
Remove from the oven, cover the chicken loosely with tinfoil and leave to rest for about 10 minutes before serving with sage and apple stuffing.