Directions:

Lemon Curd:
1) In a medium glass bowl, thoroughly whisk yolks and sugar.
2) Add lemon juice and zest and cook over a double boiler, making sure bottom does not touch the simmering water. Whisk occasionally and cook until mixture thickens and can coat the back of a spoon, 15-20 minutes.
3) Remove from heat and strain through a fine-mesh strainer into another medium bowl. Add butter, then use an immersion blender to mix until completely smooth and incorporated.
4) Strain once again and reserve 1 cup of curd in a small bowl, with plastic wrap pressed on surface. Pour remaining curd into a medium bowl and press plastic wrap on the surface of the curd. Refrigerate.

Lemon Mousse:
1) Sprinkle gelatin evnely over water in a small bowl. Let sit for 10 minutes.
2) Meanwhile, in a stand mixer set to low speed, whip cream. Gradually increase to high speed and whip to soft peaks. Store in refrigerator until ready to use (for up to 1 hour).
3) Pour gelatin set in water into a small saucepan over very low heat. Wait until all granules are dissolved, about 3 minutes.
4) Transfer gelatin to a medium bowl. Whisk in half the yogurt until no lumps remain, then repeat with remaining yogurt. Add the lemon curd. Fold in the whipped cream until no white streaks remain.

To Assemble:
1) Fit two pastry bags with Ateco 804 tips or a similar 1/2-inch tip. Fill each pastry bag about halfway, one with mousse, one wiht lemon curd (don't overfill bags).
2) Pipe about 1/2 inch of lemon curd into the bottom of each 4-ounce glass, and repeat with the mousse. Repeat until all cups have been filled, or all filling has been used. Refrigerate to chill, or, for a semifreddo effect, freeze.
3) Garnish with your favorite shortbread or butter sables.