Line the base of a slow cooker with baking parchment.
Melt the chocolate and butter in a heatproof bowl over simmering water until smooth.
Remove from heat and beat in the sugar until well combined.
Beat in eggs individually, stir in vanilla, and fold in the flour.
Pour brownie mixture into the slow cooker.
Mix cream cheese with condensed milk in a separate bowl.
Drop spoonfuls of cream cheese onto the batter and swirl with a skewer.
Cook on high for 120 to 150 minutes until a skewer comes out clean.
Lift out using the parchment and cool completely on a wire rack.
Slice into 20 squares once fully cooled.