In a small saucepan, whisk together the whole egg, egg yolks, sugar, and lemon juice.

Cook over medium-low heat, stirring constantly, until the mixture thickens, about 10–15 minutes. It will suddenly turn into a smooth, gel-like curd.

Once thick, remove from the heat and stir in the butter, one cube at a time, until melted and fully combined.

Strain through a fine sieve to remove any small bits in case the eggs were cooked.

Preheat the oven to 175℃, and line a 12 cups cupcake pan with liners.

In a small pot, combine butter, milk, oil, and vanilla. Warm gently until the butter melts, then set aside (don’t boil).

In a large bowl, beat eggs and sugar with a hand mixer for 6 minutes until the mixture triples in volume and becomes pale and fluffy.

Gently fold half of the dry ingredients into the egg mixture, then the rest — just until combined.

With the mixer on low, slowly pour in the warm milk mixture, mixing until smooth and fluid.

Divide the batter evenly into the liners (I recommend putting the batter in a piping bag to transfer the batter easily to pan without a mess), filling each about ⅔ full.

Bake for 20–22 minutes, or until a toothpick comes out clean.

Let them cool 5 minutes ivn the pan, then transfer to a rack to cool completely before adding the curd.

Prepare the syrup: In a small saucepan, combine the sugar and water. Place over medium heat and cook without stirring until it reaches 118 °C (use a thermometer).

Whip the egg whites: While the syrup is heating, start whipping the egg whites  and vanilla in a clean, dry bowl. Beat on medium speed until they form soft peaks.

Pour the syrup: Once the syrup reaches 120 °C, slowly stream it into the egg whites while beating on medium-high speed. Pour it down the side of the bowl so it doesn’t splash.