Panna cotta: Add gelatin to ¼ cups of milk, stir well, and let stand until the gelatin is dissolved. Meanwhile, place the cream, brown sugar, remaining ¼ cup milk, coffee, and vanilla in a saucepan over low heat, stirring constantly. Boil Simmer on low heat for 5 minutes. Then remove from heat and add gelatin; mix well. Spread the mixture over the chocolate mousse. Refrigerate again for at least 4 hours.