In a small sauce pan add the granulated sugar and on low heat, allow the sugar to melt and caramelize to a medium amber color (make sure all sugar is dissolved)
Once the sugar is at the desired caramel color, add in the butter and heavy cream and slowly whisk until fully combined and smooth (the caramel will get hard for a second and then will melt back down)
Remove the caramel from the heat and add in the semi sweet chocolate chips; slowly whisked until fully combined and smooth
In a small bowl, add the egg yolks
Add a small amount of the warm chocolate caramel into the bowl with egg yolks and mix until combined, add the chocolate and egg mixture back into the remaining chocolate caramel and whisk until smooth
Allow the chocolate caramel to cool completely
Using an electric mixer with whisk attachment, whisk the 1 ½ cups of heavy cream to soft peaks
Gently fold the whipped cream into the chocolate caramel mixture
Scoop the chocolate caramel mousse into bowls or cups; refrigerate until ready to serve