Preheat oven to 350° F. Grease and line a jelly roll pan with butter and parchment paper and set aside. Whisk the flour, salt, baking powder, and lemon zest and set aside.
In a large mixing bowl, add the butter and sugar and mix until light and fluffy. Add in the eggs, vanilla, lemon extract, and lemon juice and mix until completely incorporated.
Add the dry ingredients to the butter/lemon mixture and mix until just combined. Don't over mix.
Pour the batter slowly into the greased prepared pan and spread the batter with a spatula evenly into the pan. Bake for 15-18 minutes until well risen, a light golden brown color, and firm to touch.
Place a damp kitchen towel on your work surface and cover it with parchment paper. Add some confectioner's sugar which will help the outside of the sponge cake from sticking. Turn the cake out onto the parchment paper and remove parchment lining.
Using a sharp knife, cut off the firmer crusted edges from the long sides. Roll the Swiss roll starting from the short ends, making a tight turn to make a good round shape and keeping sugared paper inside of the roll. Transfer to wire rack to cool.
In a microwavable bowl, melt the butter. Add in the confectioner's sugar and lemon juice. Mix until well combined.
When the cake has cooled, gently unroll it but do not flatten it as it can crack. Spread the lemon icing on top first and then spoon the lemon curd on the icing and spread it evenly within 1 inch of the edges. Roll the cake back up again and place on a plate. Dust with confectioner's sugar. Slice and serve!