First, preheat your oven to 170℃ (325℉). Then grease a 7*7 inch baking tin with softened butter/oil and line with parchment paper, set aside.
Now to make the shortbread base, take the room temperature butter, icing sugar, flour, and vanilla essence in a bowl. Then combine everything using a spoon or simply just using your hand. Continue to bring the mixture together using your hand until the dough forms a ball.
Now pat the shortbread dough into your lined baking tin making sure it's nicely leveled and the sides are closed properly. Then prick the crust all over with a fork so it doesn't rise up while baking.
Bake the shortbread crust into your 170℃ preheated oven for about 20 minutes or until its slightly golden brown on the edges. And prepare your lemon curd filling in the meantime.
In another bowl combine the eggs, sugar, flour and lemon zest and mix until well combined. Then add the fresh lemon juice and mix again.
Take out the crust from the oven and fill with the lemon filling you just prepared.
Bake again for 25 -30 minutes or until set. Once it's baked perfectly, there should be no jiggling on top and a thin crackle crust will form on the top .
Allow it to completely cool to room temperature then refrigerate for at least 2-3 hours or overnight before serving.
Cut it into 16 small squares (or you can cut it into 9 squares if you like bigger slices) dip your knife into hot water after each cut if you like to get a clean cut every time.
Dust with some icing sugar and enjoy! You can store your lemon bars in an airtight box in the refrigerator for 4-5 days.