Electronics used for cooking
nearly all simple cookers use AC power to directly run a heating element. The elements are usually just wire coils, or sometimes flat resistance wire types. since the quantity of food being heated varies it is nearly always necessary to incorporate a thermostatic controller in order to vary the power.  On toasters this is accomplished with a simple variable timer to allow you to adjust how long the bread is exposed to the heat.  On crock pots and the like there is a variable thermostat which keeps the contents being cooked at a steady temperature. If you do use a heating element with exposed wire remember to keep it well insulated.  The coils are live power and can be lethal if you come in contact with them.  Also remember to use a thermostat which can handle the load presented to it by the heating element. If you can't easily find a thermostat for the current needed, then use a relay to handle the power.  The amount of power needed will be influenced by several factors. The quantity of food to be cooked, the size of the oven, the final desired temperature, how fast it needs to cook, and other factors.  If you look at similar sized units you can find out a good approximation of what you need by taking notes of their power needs.