Add the sugar and 1/4 cup water to a medium pot and heat over medium-high heat until the sugar dissolves. Bring to a boil and cook, without stirring, until the sugar becomes amber in color. Remove from the heat and carefully add the cream, making sure to hold the pot away from you while stirring with a rubber spatula because the cream will bubble and spit up.
Put the chocolate and butter in a large bowl. Pour the caramel mixture over the chocolate and whisk until smooth. Pour into a shallow pan and refrigerate until firm.
Roll the mixture into small truffle-size balls. Roll the truffles in the topping of your choice and garnish with a sprinkle of sea salt.