Preheat the oven to 350°F (175°C).

Pulse shortbread cookies in a food processor until finely crumbly.

Add melted butter to the shortbread crumbs while the food processor is running until fully incorporated.

Press the buttery crumbs into an 11-inch tart or springform pan, forming a crust up the sides.

Bake the crust for 15 minutes and let it cool to room temperature.

In a double boiler, combine sugar, lemon zest, lemon juice, and egg yolks.

Cook over simmering water on moderately high heat, stirring constantly, until the mixture thickens (about 5 minutes).

Remove from heat and whisk in cubed butter until melted and fully incorporated.

Strain the lemon curd mixture into a bowl using a mesh strainer.

Press a sheet of plastic wrap directly onto the surface of the lemon curd and refrigerate for at least 2 hours.

In a mixing bowl, whip heavy cream until firm peaks form.

Fold the whipped cream into the chilled lemon curd to create the mousse.

Return the lemon mousse to the refrigerator.

Once the crust is fully cooled, spread raspberry jam evenly over the base.

Gently pour the lemon mousse over the raspberry jam layer and smooth the top.

Refrigerate the tart for at least one hour to allow it to fully set.

Decorate the tart with whipped cream and fresh raspberries before serving.