Gently melt the butter in a microwave or a small pan (do not allow to brown) and use some to coat one side of the chicken portions. Place the chicken, buttered side up, on a grill pan (broiler pan) and cook slowly at low heat. When turning the chicken portions, coat the other side in butter to give a nice golden appearance. An average portion of chicken will take about 20-25 minutes to cook in this way, although a simple leg of chicken will take a little less (about 15 minutes).
If you want to use a cook's thermometer, chicken is fully cooked when the chicken breasts reach 70ºC - 160ºF at their thickest part, and the legs/thighs reach 77ºC - 170ºF.