In a clean Thermomix bowl, add the hot water and heat for 3 minutes, 90 degrees, Speed 2.
Add the jelly crystals and gelatine and mix on Speed 2 until they have dissolved. Pour jelly into another bowl and allow it to cool until it has reached room temperature.
Remove the slice from the fridge and arrange the strawberries over the top of the slice – gently push them into the slice to help stop them moving when you add the jelly.
Carefully pour the jelly over the slice and place it back in the fridge to completely set approximately 6 hours. If possible, let it set overnight.
Remove the set slice from the fridge and using a hot knife, cut into squares.