In a large bowl, using an electric hand mixer, beat the cream cheese, pumpkin purée, brown sugar, 1teaspoon pumpkin pie spice, and vanilla until it becomes smooth and creamy.
In another large bowl, using an electric hand mixer, beat 2 cups of the cream until it forms soft peaks. Add 1/4 of the whipped cream to the pumpkin mixture and stir to lighten it. Gently fold in the remaining whipped cream. Spoon the moose into dessert glasses, cover, and refrigerate for at least 2 hours or overnight.
When you are ready to serve, whip the remaining cream with the sugar. Top each mousse with a dollop of whipped cream and a sprinkling of the remaining 1/2 pumpkin pie spice.