Switch on the oven to 200 °C and warm up the roasting pan in it. Frying. This is a most difficult and important step and it should be taken seriously. It is very important to use heavy cast iron skillet.
Cooking should be started on slightly oiled, preheated to the high temperature cast iron skillet and heavy lid, and the temperature should be reduced to the medium during cooking. Start to fry from the external, skin side, to melt the fat. Fry under the lead on each side for 2 minutes (5 sides in total), then fry 1 minute on each side, and then fry 30 seconds on each side. In the rib side you can fry for a bit longer, for example 3, 2, and 1 minute. Be careful, to do not burn the fat to a very black state. Also during cooking, add some thyme to lamb and rid out of fully fried thyme.