You will need one 12-by-12-inch piece of slate (available in the flooring section of your local hardware store). It can be up to 1/2 inch thick. Be sure to rinse slate with water and dry before using.
Step 1: Seasoning
It is important to season the slate before cooking with it, as the slate will crack if it is heated too quickly. To do so, rub slate with vegetable oil and place in oven; turn oven temperature to 400 degrees. Slate will begin to warm up as the oven starts to reach its set temperature. When oven reaches 400 degrees, let slate stand in oven for about 5 minutes before transferring slate to a gas burner.
Step 2: Preheating
Once slate has been seasoned, carefully place it directly over a gas burner on a stove. Heat over medium heat, slowly increasing the heat to medium-high.
Step 3: Cooking
The best items to cook on slate are any fish without skin (such as tuna or monkfish), beef, or skinless chicken. Oil and season item to be cooked as desired, and place directly onto the slate. Cook until it has reached degree of doneness; transfer to serving platter. Turn off heat, and let slate stand on burners until cooled. If slate has cracked during the cooking process, discard.