Combine the sugar, eggs, lemon juice & zest, butter and salt in a small nonstick or enameled (NOT metal) saucepan over medium-low heat.

Whisk continuously until it thickens, about 5 minutes, just until it reaches about 170F (77C) - don't go over. It should be thick enough to coat the back of a spoon.

While it’s still hot, press the curd through a sieve into another bowl/jar, cover it and allow it to cool completely to room temperature. Store leftovers covered in the refrigerator.

In a small pot, over medium heat, cook the butter for 5-10 minutes, stirring intermittently until it begins to bubble and foam.

Then stir continuously until you see the milk solids browning and settling on the bottom. Pour the butter into a bowl and allow it cool for a few minutes. If measured now, 113 grams of butter should now measure 93 grams. Refrigerate for a few minutes.

Place the sugar into a medium-large bowl and zest the lemon on top. Use your fingers to massage the lemon zest into the sugar to release the oils.

Add the butter to the sugar and whisk until they're completely combined.

Then add the egg yolks, lemon juice and vanilla and whisk together aggressively for 2-3 minutes, until it's smooth and has lightened in color.

Add the flour, salt and baking powder and fold the cookie dough just until there are no more streaks left of flour.

Freeze cookie dough for 15-30 minutes or refrigerate for about an hour. Scoop eight 2 ounce cookies and roll between your hands to get smooth cookie dough balls. Place on a lined baking sheet (they spread a lot).

Preheat oven to 350F (177C) and bake one sheet on the middle rack for 10ish minutes, remove, bang on the counter, use a round biscuit cutter to scoot them around so they’re round again and return to the oven for another 4ish minutes, just until the edges are starting to brown.

Remove from the oven. The edges should be lightly browned and the top slightly puffed and no longer wet. Give it another quick tap on the counter & scoot them around again so they’re perfectly round.

Use a tablespoon or small cup to make a slight indent in the center of the cookies to contain the lemon curd.

Allow to cool completely and then spread about 1 tablespoon of lemon curd onto each cookie.

Bring a small pot with a little water to a boil and then reduce the heat to simmer (keep it on very low heat).

Wipe down your equipment with a tiny bit of vinegar or lemon juice (any edible acid) and then place the sugar and cream of tartar in the bowl of a stand mixer, whisking them together.

Add the egg whites to the bowl and whisk the egg whites into the sugar. Place the bowl of egg whites and sugar on top of the simmering water (making sure it doesn’t submerge into the water) – you want the steam to heat the egg whites.

Whisk the egg whites frequently so they don’t coagulate around the edge of the bowl. Generally around 5 minutes, the sugar will feel like it’s dissolved in the egg whites but you want to take the egg whites to 175F (80C) in order to get that stable, marshmallowy texture, which is normally around 10 minutes for me. So make sure to check the temperature with a thermometer between the 5-10 minutes (it may take up to 15 minutes).

Once it’s at 175F (80C), turn the stove off, remove the bowl from the simmering pot and place it on the stand mixer fit with the whisk attachment. Beat at medium speed for a minute and then increase to medium-high for about 10 minutes.

Add in the vanilla extract and salt and mix, that just until it’s combined, making sure to scrape the edge of the bowl as well. The texture should be thick and marshmallow – not dry or foamy.

Pipe on top of the cookie and lemon curd and use a culinary torch to toast the meringue.