Once you have cleaned and cut the strawberries, place them in a bowl and sprinkle them with sugar and the Cointreau. Mix them gently with a spoon so that the sugar and alcohol is well distributed. Cover the bowl with plastic wrap and place it in the refrigerator for at least 20 minutes and up to 4 hours. The sugar and alcohol cause the strawberries to “macerate,” softening them a bit and making them juicy.
In a clean, cool bowl, whip the cream until soft peaks begin to form. Add the brown sugar a few teaspoons at a time, whisking it in after each addition. When all the sugar is incorporated continue to whip until the cream is fully whipped and nice firm peaks form. Add the sour cream, the vanilla extract and the seeds from half of a vanilla bean. Whip them in thoroughly. Refrigerate until you are ready to serve.