Instructions

For the shortbread crust

1. Preheat oven to 350 F. Line a 9x13 inch pan with parchment paper. Set aside.
2. In the bowl of your stand mixer, beat the butter and sugar together until creamy. Slowly add in the flour and sea salt, mixing until a crumbly dough forms. 
3. Press the dough into the prepared 9x13 pan as evenly as you can. Bake for 18-20 minutes or until just golden brown. Don't let it cook too long! You don't want it to be too crumbly. Let cool completely while you work on the next steps.

For the lemon curd

1. Zest the lemons and then juice them. You will need about 1/4 cup of lemon juice (if you have any extra lemon juice, save it for the lemon mousse). Set aside. Reserve about 1 tbsp of the lemon zest for garnishing the cakes.
2. In a heat-safe bowl that is the right size to set on top of a sauce pan (or a double boiler if you have one), whisk the eggs. Add the sugar and whisk until combined. Stir in the lemon juice and lemon zest. Fill your sauce pan with about an inch of water and bring to a simmer. Place the bowl of lemon mixture over the sauce pan and stir until thickened, about 10 minutes.
3. Cut your butter into slices and add one slice at a time, stirring until melted. Once all the butter has melted, strain the curd. Place in a storage container and refrigerate until cooled. You will need 1/2 cup of curd when you make the lemon mousse in the next step. You may have extra, so you can use the extra in another recipe or even eat it plain, it's so good!

For the lemon mousse

1. Pour the lemon juice and water into a small bowl. Whisk in the gelatin and let sit for 5 minutes so that it blooms. 
2. Meanwhile, in the bowl of your stand mixer with the whisk attachment, whip heavy cream until soft peaks form. Add in about a third of the powdered sugar, whip again until soft peaks form. Set aside. 
3. Switch out the bowl on your stand mixer for a new one, and in this bowl beat the cream cheese until smooth and fluffy. Mix in 1/2 cup of the lemon curd that you made in the previous step and the remaining powdered sugar. 
4. Microwave the gelatin mixture for 15 seconds or until it is liquid again. 
5. Turn on the mixer with the bowl of cream cheese mixture to a slow speed. Pour in the gelatin and blend until combined. 
6. Turn off the mixer and remove the bowl. Use a spatula to gently fold 1/3 of the whipped cream mixture into the cream cheese mixture, then add in the rest of the whipped cream and fold until combined. 

Assembly

1. Use a small mason jar or glass cup with straight sides to make cut 8 circles out of the shortbread. You should use something that makes a circle that is the same size as the openings of your silicone molds or just a bit smaller. Set the shortbread circles aside.
2. Place your silicone molds on a baking sheet (if you don't have this, see the alternate instructions in the notes below for using ramekins). Fill 8 of the cavities of your silicone mold with the lemon mousse almost to the top. 
3. Place 1 shortbread circle at the top of each mousse-filled cavity, pressing down just a bit. Place the baking sheet with the silicone molds on it into the freezer to set for 2-3 hours.  

For the mirror glaze

1. Once the cakes are close to being done in the freezer, get started on the mirror glaze. Whisk together the powdered gelatin and cold water. Set aside to bloom. Place the white chocolate chips in a medium sized bowl and set aside. 
2. Place sweetened condensed milk and sugar in a saucepan. Bring to a bowl and then remove from the heat. Stir in the gelatin mixture until it is dissolved.
3. Pour the saucepan mixture over the white chocolate chips. Let sit, stirring occasionally until the chocolate is melted, about 5 minutes. Use an immersion blender to blend until smooth. Pour the glaze through a sieve to remove any lumps. Let cool for a few minutes until just above room temperature. 
4. Line a baking sheet with parchment paper and place a cooling rack on top of the parchment paper. One the mirror glaze is ready, take the silicone molds out of the freezer. Pop the cakes out of the mold and place them on the cooling rack. Pour the mirror glaze over the cakes. Transfer to a serving tray and place in the refrigerator so that the mirror glaze can set and the cakes can thaw, about an hour. Take the cakes out of the refrigerator for about 10 minutes before serving so that the shortbread isn't too hard.