In a medium saucepan, heat the milk over medium-low heat just until it’s steaming. Turn heat down to low until ready to use.

In a large bowl, add the egg yolks, sugar, lemon zest, salt, vanilla, and cornstarch and whisk until combined and a pale-yellow color.

Add in ¼ of the heated milk while stirring vigorously. Then, add the rest in and stir to combine.

Transfer the mixture to the saucepan. Heat over medium-low heat, whisking continuously, until the mixture is thick and soft peaks form, about 8-12 minutes.

Remove the pastry cream from the heat, add the butter, and mix to combine. Place plastic wrap directly on top to prevent a skin from forming. Chill in the fridge until completely cold.

Combine the sugar and lemon zest in a bowl for the lemon sugar. Set aside.

Preheat the oven to 350 degrees F (175 degrees C). Line two cookie sheets with parchment paper.

In a large bowl, whisk together the flour, baking powder, baking soda, and salt. Set aside.

In a large bowl, cream together the butter and granulated sugar using an electric mixer on high speed until fluffy, about two minutes.

Add in the egg, vanilla, and lemon zest, and mix on medium speed until pale in color and fluffy, 1-2 minutes.

Slowly add the dry ingredients. Mix on low speed just until the dough pulls together.

Scoop the dough into balls using a large cookie scoop. Roll into balls, then roll each ball in the lemon sugar.

Place the dough on the parchment-lined cookie sheets and slightly flatten each ball. Bake 6 cookies at a time.

Bake the cookies for 9-10 minutes. Let them cool on the baking sheet for 5 minutes, then transfer to a cooling rack.

Transfer the pastry cream to a piping bag fit with a small circular tip. Once cooled, pipe pastry cream on top of each cookie.

Sprinkle about 1 teaspoon of sugar over each and use a kitchen torch to brûlée the sugar until golden brown.

Let the cookies cool for 10 minutes after torching before serving.