Combine the egg yolks, lemon juice, 1/4-cup sugar, and lemon zest in a large bowl and mix well.
Beat the egg whites in a medium mixing bowl until foamy. Add the cream of tartar and salt and beat until soft peaks form. Add 3/4-cup sugar gradually and beat until stiff and glossy.
Whip the cream in a bowl until stiff.
Fold the egg whites and whipped cream gently into the egg yolk mixture.
Spoon into a bowl. Freeze, covered with foil, for 8 hours or longer.
Let the mousse stand in the refrigerator for 1 to 2 hours before serving. Spoon into 12 dessert dishes and garnish with fresh berries and a spring of mint.