Place the cream in a saucepan and heat almost to boiling.

In a separate pot, heat sugar over medium heat until it becomes amber-colored caramel. Don’t mix, just shake the pot from time to time.

Carefully add the hot cream to the sugar, stirring with a wooden spoon. Continue stirring until you have a smooth toffee. Remove from heat. Let sit two minutes to cool off slightly, then add the butter. Stir until incorporated. Cool to room temperature.

Beat the heavy cream until stiff.

Add condensed milk and vanilla and beat another few seconds until incorporated.

Pour half the ice cream into a nine- by 13-inch (20- by 30-centimeter) pan. Pour toffee on top and mix a bit for a marble effect.

Cover with the remainder of the ice cream and freeze until completely firm. Cut into one- and- a- half-inch (four-centimeter) squares.

Heat oven to 225 degrees Fahrenheit (110 degrees Celsius).

Spread the chocolate on a lined baking sheet and place in the oven for 20 minutes. Remove from the oven after 10 minutes and stir. Return to oven for another 10 minutes, then remove and stir again. If the chocolate is caramel colored, remove from the oven and stir until smooth. If not, return to the oven for a final 10 minutes.

When the chocolate is caramel colored and smooth, add the cocoa butter or oil and stir well. Cool to 95 degrees Fahrenheit (35 degrees Celsius).

Dip ice cream squares into the chocolate mixture and turn to coat. Return to freezer. Serve frozen.