To make the mochi balls:
1) Combine the rice flour, wheat starch, sugar, butter, and salt in a mixing bowl. Mix together and then add the boiling water. Stir with a spoon, and then knead with your hands to form a smooth paste. Wet your hands and form the dough into 2cm diameter balls, and then roll them in the sesame seeds.
To make the caramel:
1) Put the sugar and water in a large saucepan over high heat and stir. Bring to a boil without stirring and cook, still without stirring, until the sugar becomes a deep brown caramel. Do not stir at any point after the pot is placed on the stove or the sugar will crystallise. Add the cream and salt and cook until reduced by one-quarter. Add the brandy when the sauce is almost done reducing.
2) Put enough soybean oil in a saucepan to come 7cm up the sides of the pan and heat to 175C. Lower the mochi balls into the oil and fry until golden brown, about 4 mins. Drain on a paper towel. Serve on a plate with the warm caramel in a dipping sauce bowl on the side.