Place the eggs, salt and caster sugar in your mixer bowl. Start whisking on low, gradually increasing until whisking on maximum
Continue whisking until the eggs are at ribbon stage; if the whisk leaves a trail that lasts for 10–15 seconds when lifted from the bowl.
Place the plain flour, baking powder and lime zest in a bowl and mix together. Sprinkle half of this mixture over the eggs and fold through using a large metal spoon.
Add the remaining flour and gently fold through until incorporated. Drizzle the melted butter down the side of the bowl, gently folding through until incorporated.
Pour the batter into a 23cm (9in) springform cake tin. Tap the tin gently on your worktop once, place in a preheated oven at 190°C / 170°C (fan) / gas mark 5. Bake for 35–45 minutes or until the cake is well risen and a skewer comes out clean.
Remove the tin from the oven and place upside down on a board. Leave until cool before removing from the tin and slicing into three even layers.
For the gin syrup: Put the water, sugar, lime juice and juniper berries in a pan, boil for around five minutes. Add the gin and thinly sliced lime, turn off the heat and leave until cold.
Pour through a sieve and reserve the lime slices
For the frosting: put the icing sugar, butter and 50ml of the gin syrup in a mixing bowl, whisk until light and fluffy.
Brush each layer of cake with the remaining gin syrup. Assemble, spreading frosting between the middle layers.
Cover the sides and top of the cake with frosting before using a serrated knife or icing comb to create a pattern. Decorate with thesyrup-soaked lime slices.