In a medium bowl, add softened butter, oil, all the ground spices, sugar, salt, dried mint, ginger & garlic and lemon juice.
Using a spatula or spoon, mix until combined. Your masala compound butter is ready. We will use about 75 g over chicken and save the rest. Shape the leftover butter into a log using plastic wrap, refrigerate, and slice off pieces as needed.
Place your spatcock chicken on a kitchen board or a baking sheet and using your fingers, slightly loosen the skin over the breast and thigh areas.
Using a spoon, stuff a tablespoon of the masala butter under the skin on thigh & breast areas. Press gently to spread the butter (should be easy since butter is softened) so that it gets into all the nooks.
Rub the remaining masala butter all over the surface of the chicken, including the underside. Marinate the chicken for at least 3 hours (though overnight is the best).
Preheat your oven to 450F. Position the buttered chicken, breast-side up, over a roasting rack. Tuck the wings securely beneath or on top the bird, then loosely cover the baking tray or pan with aluminium foil.
Roast the chicken until golden brown, removing the foil after 40 minutes. Continue roasting until an instant-read thermometer inserted into the thickest part of the breast reads 165°F, about 55 minutes to 1 hour and 5 minutes.
Transfer the chicken to a carving board and let it rest for at least 10 minutes before carving. Carve the chicken and garnish with a sprinkle of fresh cilantro. Serve.