Combine the ingredients. Add the self-rising yellow cornmeal mix, cold butter, sugar, and salt to a mixing bowl.
Add the boiling water. Bring water to a boil, then measure out ½ cup and pour it into the bowl. Stir until the butter melts and everything comes together into a thick dough. The dough should hold together with little to no crumbs sticking to your fingers.
Let the dough rest. Allow the dough to sit for 5 minutes while preparing the skillet.
Heat the oil. Pour approximately ¼ cup of frying oil into a 10-inch cast-iron skillet, or enough to cover the bottom. Heat over medium-low heat. The oil should produce a gentle sizzle when the cornbread is added.
Shape the cornbread. Divide the dough into six portions weighing approximately 50–60 grams each. Roll each portion into a ball, then flatten it into a patty about ½ inch thick.
Fry the first side. Place the cornbread into the heated oil. You should see a few small bubbles around the edges. Continue shaping and adding the remaining patties as space allows. Fry for approximately 3 minutes, until the edges begin to firm up and the bottom is crisp enough to support the patty without bending when lifted.
Flip and finish cooking. Carefully flip the cornbread and fry for approximately 3 more minutes, until golden brown. The center should feel firm rather than soft or wet. Remove from the skillet and repeat with any remaining patties.
Serve immediately. Hot water cornbread is best enjoyed fresh from the skillet while the outside is still crispy.