Preheat oven to 325 F.
In a large bowl, cream together butter and sugar.
Mix in the eggs one at a time.
Mix in the vanilla extract and lemon extract, lemon zest and lime zest.
Gradually add in the flour and salt and mix until combined.
Mix in the heavy whipping cream and 7UP until well combined and batter is fluffy.
pour into 4 inch round cake pans - (it make 5 using a 3 inch tall pan) or in a 9x13 pan (you'll have to cut the circles out later)
bake until the center is set - the 9x13 pan will take about 40 mins - for the 4x3 round pans - beause there is so much batter and height its a little tricky - I baked it at 425 in a water bath (4 inch pans placed inside another pan with water in it) for 40 mins, then pulled the pans out of the waterbath and baked at 410 for another 30 mins - to try to cook the inside and outside evenly
let cool or freeze - level the top and bottom and cut each cake in half - I also ended up cutting the outer edge to fit into the chocolate shell - you'll need SIX 4 inch circles each about 1 1/4 inch tall
brush with the 7UP syrup for an even stronger flavor