In a heavy saucepan, bring all the ingredients to a boil, except for the butter, stirring to dissolve the sugar. Attach a candy thermometer in the centre of the pan and simmer, without stirring, until the thermometer reads 112 °C (234 °F). Remove from the heat and place the pan in an ice water bath. Let cool, without stirring, until the thermometer reads 43 to 50 °C (110 to 122 °F) or 20 to 30 minutes.
Remove the pan from the water. With an electric mixer, beat the mixture until it loses its gloss but is still soft, about 2 minutes.
Beware, the next step must be done quickly. Spread three-quarters of the sugar fudge on the unrolled cake. Roll again. Set aside.
Continue to beat the remaining sugar fudge and add the butter, one or two cubes at a time, beating until smooth. If necessary, refrigerate for 5 to 10 minutes or until the buttercream is spreadable. Place the log on a serving dish and frost with the sugar fudge buttercream. Store at room temperature.
Note from Ricardo
Beware; this dessert is for serious sweet tooth!
