First, make the lemon curd. In a stainless steel bowl placed over simmering water, whisk together the eggs, sugar and lemon juice until blended. Cook, stirring constantly. This is really important, otherwise you risk the chance of it curdling. Continue to stir until it becomes thick. This will take between 5-10 minutes. Once it has reached a lovely thick and creamy texture, immediately remove from heat. Put through a fine strainer to remove any lumps. Cut in the butter and give a good stir. Set aside.
Line a 12 count medium sized muffin pan with muffin liners. Preheat your oven to 350 degrees F/180 degrees c.
In a medium bowl, combine the flour, baking powder, salt and lemon zest. Stir to combine and set aside
Next, in your mixing bowl, cream the butter and sugar until light and fluffy, about 3 minutes. Now beat in the eggs one at a time until they are completely incorporated. Whisk in vanilla extract.
Next, add 1/2 of the flour mixture and gradually incorporate it into the batter. Next add all the milk and combine. Add remaining flour mixture along with the lemon zest and stir until just combined.
Fill your muffin tins evenly with half of the batter. Then put a spoonful of the lemon curd over the batter in each muffin tin. Spread it out and then top with remaining batter. Evenly sprinkle over remaining 3 tablespoons of sugar.
Bake for about 18-20 minutes. Remove from oven place on a cooling rack to cool for about 5 minutes.
Remove from baking pan and serve warm.