Place the first five ingredients in a large bowl and mix together with a wooden spoon or whisk until smooth.
Stir in the chopped chocolate.
In a separate small bowl, mix the Philadelphia with 3 tsp of caster sugar until soft.
Pour the chocolate mixture into a silicon (or metapan in a larger slow cooker, or for a smaller slow cooker e.g. 3.5 litre, pour it into your slow cooker pot lined with baking paper and greased in case any mixture escapes.
Dot the sugared Philadelphia on top and marble it with a knife.
Put the lid on, and cook on high for approx. 1-2 hours until firm round the edges with a wobble left in the middle. Or cook until completely firm if you like your brownies without the gooey-ness.
The cooking time depends on your own slow cooker and how hot it runs so check regularly and watch out for burning!