Prepare the wet ingredients. In a liquid measuring cup, add and measure melted butter, vegetable oil, milk, lemon zest and pure vanilla extract. Mix until blended. This will let the lemon zest infused and will not dry out while preparing other ingredients.
For the egg yolk mixture. In a medium-sized bowl, whisk the egg yolks, granulated sugar and lemon juice until egg yolks are pale in colour and sugar is almost dissolved.
Weigh, measure and sift the dry ingredients. Weigh the cake flour or spoon in a measuring cup and level it off with a spatula. Sift in a strainer over parchment paper with the baking powder and salt.
Mixing the dry and wet ingredients. Add in egg yolks mixture in 4 additions alternately with the wet ingredients. Mix until blended.
For the meringue. Whisk the egg whites gradually add sugar and whisk until medium-stiff peaks.
Mixing the cake batter and meringue. Add the meringue to the cake batter in four additions. Cut and fold and avoid over mixing.
Scoop the cake batter to portion evenly. Line the 12-muffin pan with muffin paper liner. Scoop and portion evenly about 3/4 full using an ice cream scoop with the trigger.
Bake the cupcakes. Bake in preheated oven to 375°F for about 12 to 15 minutes or until the toothpick inserted comes out clean. Let it cool in a pan for 10 minutes.
For the lemon syrup. Mix the sugar and lemon juice in a small bowl and microwave for about 15 seconds or until sugar is dissolved. While the cupcakes are still hot in the muffin pan, brush the top of each cupcake with lemon syrup. Transfer on a cooling rack to cool completely.