Preheat the oven to 325F.
Add the lemon zest and sugar to the bowl of a stand mixer. Mix on high to help the zest release it’s oils.
Add the butter and beat until well combined with the sugar, light and fluffy.
Add the eggs, one at a time, beating well between additions.
Stop the mixer and add the lemon juice, vanilla, milk and wheat beer, stir until combined.
Add the flour, baking power, and salt, stir until just combined.
Grease and flour a 9X13 baking dish, pour the batter into the pan in an even layer. Bake at 325 for 35-40 minutes.
Remove from oven allow to cool.
In a large bowl add the lime zest, powdered sugar and cream. Beat with a hand mixer on high until soft peaks form. Add the rum and lime juice, beat until well combined.
Frost the cake with the whipped cream. Chill until ready to serve.