The longest part of the process is boiling the sugar syrup, so you should start the sugar syrup first.  Stir 2 cups (or ½ liter) of sugar together with 2/3 cups (or 167 ml) of water in the first small cooking pot over high heat.  If your two pots are of different sizes, this should be the smaller of the two.  Use the heat-safe mixing spoon.  This spoon will be needed again for a later step.  The sugar won't all dissolve at first, but as the water heats up, its solubility will increase.  Once the water is at a rolling boil, the solution should become fully transparent.  If it isn't, add slightly more water, though this may increase the time it takes to prepare the sugar syrup.

Once the sugar syrup is at a rolling boil, stop mixing and let it boil.  As some of the water boils off, the boiling point will increase due to the higher concentration of sugar.  This allows the sugar syrup to gradually become more concentrated.

While the sugar syrup is boiling, now is the best time to melt the butter.  Put the 1 lb (or ½ kg) of unsalted butter into the second small cooking pot and place over high heat.  Once the butter is melted, add the ½ lb (or ¼ kg) cocoa powder to the butter and mix thoroughly with the same mixing spoon.  It's perfectly fine to use the same spoon as you used for the sugar syrup, as the sugar syrup will soon be mixed in as well.  Then, lower the heat to a simmer or remove from the heat completely.

Apply a thin layer of oil to the ice cube tray, either using the brush or any other means of applying a thin layer.

After the sugar syrup has been boiling for about five minutes, fill a glass with cold water, then spoon out a small amount of sugar syrup into the cold water.  If the syrup hardens completely, it's ready.  Remember, butter is liquid at room temperature.  To make the chocolate solid and hard, the sugar syrup must be sold and hard at room temperature.  The consistency of the chocolate will be somewhere between the consistency of butter and the sugar syrup.  If the syrup isn't solid when submerged in cold water, wait some more time and try again.

Once the syrup is ready, mix it into the chocolate/butter mixture.  Optional technique that requires two people:  If one person slowly adds the sugar syrup while the other person quickly stirs the butter/cocoa mixture, and the butter/cocoa mixture is at room temperature, the syrup will form long, thin crystals which can solidify, have sharp edges, and cut holes in the fat, mixing in air during mixing, to create an aerated chocolate.  This is called folding the sugar syrup in to cream the fat.

Once the sugar syrup is fully mixed into the chocolate, pour it into the ice cube tray.

Place the ice cube tray into the refrigerator for two hours to cool.

Once the chocolate cools, the chocolates should relatively easily come out of the tray.