Preparation

Make the mousse

• Set a strainer over a bowl and line with two layers of damp cheesecloth or paper towels, allowing a few inches of overhang. Spoon in the yogurt,cover with the cheesecloth overhang or another paper towel, and refrigerate until thick, creamy, and reduced by half, 3 to 4 hours.
• In a small skillet, combine the honey, 2 Tbs. water, and 1/8 tsp. salt. With the tip of a paring knife, split the vanilla bean lengthwise and scrape the seeds into the skillet. Add the bean, too. Bring to a boil over medium heat, stirring constantly until the honey melts. Boil vigorously for one minute, swirling the skillet, then remove from the heat. Cool to room temperature, about 15 minutes. Remove the vanilla bean.
• In a stand mixer fitted with the whisk attachment or using a hand mixer, whip the cream to soft peaks. Add the yogurt and continue whipping on medium high until very thick, about 1 minute. With the mixer running, slowly pour the cooled syrup down the side of the bowl. Whip for 2 minutes longer to incorporate plenty of air. The mousse will be very fluffy, but will not hold a firm peak.
• Divide among 4 dessert glasses or small bowls. Cover and chill until very cold, 2 to 4 hours.

Make the balsamic berries

• In a small saucepan, combine the balsamic vinegar, honey, and 1/4 tsp. pepper. Set over medium heat. Bring to a boil, stirring for the first minute to dissolve the honey. Continue boiling, swirling the pan, until the syrup is reduced to 1 to 2 Tbs., 3 to 4 minutes. It will be quite thick and sticky. Scrape over the berries, and stir gently to coat.

Assemble

• Divide the balsamic berries among the mousse glasses. Garnish each serving with a crumbled amaretti cookie.