In a small saucepan, whisk together egg yolks, 1/4 cup lemon juice, and 2 tbsp granulated sugar until well combined.

Cook over medium-low heat, whisking constantly, until the mixture thickens enough to coat the back of a spoon (about 5-7 minutes). Do not boil.

Remove from heat and stir in the cold butter and 1/2 tsp lemon zest until butter is melted and incorporated.

Transfer the lemon curd to a small bowl, cover with plastic wrap pressed directly onto the surface to prevent a skin from forming, and chill in the refrigerator for at least 30 minutes, or until completely cold.

In a large mixing bowl, using an electric mixer, beat the softened cream cheese on medium speed until smooth and creamy, about 1-2 minutes.

Add 1/2 cup granulated sugar, 1/4 cup fresh lemon juice, 1 tbsp lemon zest, and vanilla extract. Beat until well combined and smooth, scraping down the sides of the bowl as needed.

In a separate large, chilled mixing bowl, pour in the cold heavy cream and powdered sugar.

Using an electric mixer with whisk attachment, beat on medium-high speed until stiff peaks form. Be careful not to overbeat, or it will turn into butter.

Gently fold about one-third of the whipped cream into the cream cheese mixture until just combined to lighten it.

Add the remaining whipped cream and gently fold until no streaks remain, being careful not to deflate the mousse.

Spoon or pipe the lemon cheesecake mousse into individual serving glasses or ramekins.

If using the lemon curd, drizzle or dollop spoonfuls of the chilled lemon curd over the mousse. Use a skewer or knife to gently swirl the curd into the mousse for a marbled effect.

Alternatively, layer the mousse and curd for distinct layers.

Cover the serving glasses with plastic wrap and chill in the refrigerator for at least 2-4 hours, or until set. For best results, chill overnight.

Before serving, garnish with fresh berries, extra lemon zest, or a sprinkle of crushed cookies, if desired.