Make the tart shell:

1. In a bowl, rub together the butter, flour and sugar until crumbly

2. Mix in egg yolk, salt, and just enough cold water to form a dough.

3. Flatten into a disk, wrap in plastic, and chill for at least 30 minutes.

4. Roll out the dough to fit your tart pan and line it. Prick base with a fork.

5. Chill again for 15 minutes, then bake at 350° F (175°C) for 20-25 minutes or until golden. Cool completely

Make the lemon curd:

1. In a saucepan, whisk together eggs, sugar, lemon juice and zest.

2. Cook over medium heat, stirring constantly, until thickened and can coat the back of a spoon (~8-10 minutes)

3. Remove from heat and stir in butter cubes until smooth.

4. Pour the lemon curd through a fine-mesh strainer into a clean bowl (this removes any tiny scrambled egg bits and the zest if you want an ultra-smooth texture.

5. Stir gently to combine, then let it cool slightly before pouring into the baked tart shell.

6. Chill in the frige to set (2+ hours)

Italian Merengue:

1. Before you start with your italian merengue, make sure your mixing bowl and whisk are completely grease freee. Wipe them down with a small amount of vinegar or lemon juice and dry thorougly. Any grease or residue can prevent the egg whites from whipping properly and will affect stability.

2. While the syrup is cooking, begin whisking the egg whites with the cream of tartar in a stand mixer or large bowl.  

3. When syrup reaches 244-250° F (118-121°C) slowly pour in a thin stream along the side of the bowl (avoiding the whisk) into the egg whites while mixing on medium.

4. Whip until glossy, stiff peaks, and bowl is just warm (5-7 minutes)

5. Optional: Sift in 10-15 g powdered sugar once warm (not hot) and whip for another 20-30 seconds for extra shine and stability

Pipe or spread merengue

1. Choose your style: rustic swirls, rosettes, dots, or tall spikes.

2. Pipe directly over the chilled curd.

3. Torch lightly for golden tips or leave white for a cloud like finish