Preheat oven to 350°F (175°C) and lightly grease a 12-cup muffin pan.
In a large bowl, cream butter, brown sugar, and granulated sugar until light and fluffy.
Beat in eggs one at a time, then mix in vanilla extract until smooth.
In another bowl, whisk flour, baking soda, and salt together. Gradually add to the wet mixture until just combined.
Fold in mini chocolate chips, being careful not to overmix.
Scoop about 2 tablespoons of dough into each muffin cup and press gently into the bottom and sides to form a cup shape.
Bake for 13–15 minutes, or until golden brown and set.
Remove from oven and use a small spoon to gently press down the centers while still warm to maintain the cup shape. Cool completely before filling.
For the cheesecake mousse, beat cream cheese and sugar together until smooth.
In another bowl, whip heavy cream and vanilla until stiff peaks form. Fold into the cream cheese mixture until light and fluffy.
Spoon or pipe the mousse into cooled cookie cups.
Drizzle with chocolate sauce before serving, if desired.