Place the brown sugar, butter, cream and vanilla extract into the Thermomix bowl. Cook forĀ 9 min/Varoma/speed 2, with the simmering basket (or splatter guard) on the lid instead of the measuring cup.
Leave the sauce to cool for a few minutes before serving, as it will continue to thicken while cooling.
Notes
Extra-smooth sauce: For an ultra-smooth finish (especially when using it in desserts like panna cotta), strain the sauce while still warm through a fine-mesh sieve to remove any tiny sugar crystals.
Storage: Store the sauce in an airtight jar in the fridge for up to 2 weeks. It also freezes well. Allow it to cool, then pour into a freezer-safe container (leaving a little room at the top) and freeze for up to 3 months. Thaw in the fridge, then reheat gently, stirring until smooth.