Tangerine Orange Mousse

From 6 Bittersweets recipe shared on Pure Joy Events Blog
Slightly adapted from the New York Times
Serves about 6 to 8

XIAOLU'S NOTES: If you don't have orange-flavored liqueur on hand or want to keep this non-alcoholic, you may substitute 2 tablespoons of orange juice concentrate (undiluted) in place of the liqueur.

Zest of 2 tangerines, to garnish
2/3 cup tangerine juice (from about 3 to 4 tangerines)
1 package (1/4-ounce) unflavored gelatin (such as Knox brand)
3 Tbsp lukewarm water
2 Tbsp Cointreau, Grand Marnier, OR other orange-flavored liqueur
5 large eggs, separated
1/3 cup sugar
1/4 cup freshly squeezed lemon juice
1 cup heavy cream, cold

Wash and dry 2 tangerines, then zest them (being careful to stop before you reach the bitter white pith underneath). Store zest in a covered container and set aside for garnish. Slice 3 tangerines (including the 2 zested ones) in half and squeeze their juice into a bowl. Strain the juice to remove pulp and seeds, then transfer into a measuring cup. If there is less than 2/3 cup, then juice a 4th orange until you have 2/3 cup tangerine juice in total. Set juice aside. In a separate small bowl, dissolve the gelatin in 3 tablespoons of lukewarm water and add the orange liqueur (or orange juice concentrate); set aside.

Place the egg yolks in a heavy saucepan and add zest, gelatin mixture, sugar, lemon juice, and tangerine juice. Mix well, using a wire whisk. Place the saucepan over very low heat (you may also use a double boiler) and whisk gently until the mixture has thickened enough to coat the back of a spoon (like in this photo). Be careful not to overcook the egg mixture. Transfer to a large mixing bowl and let cool completely.

Transfer the cream into a chilled, medium-sized bowl. Whip with an electric mixer until the cream holds stiff peaks. In a separate bowl (must be completely free of oil or fat), whip the egg whites until barely stiff (should be just past soft peaks and not yet too dry). Fold whipped cream into the cooled egg-tangerine mixture. Gently fold in the egg whites until just barely blended.

Place the mousse in individual bowls or glasses or in a serving bowl. Chill overnight or for at least 4 hours.