Whip the cream on high speed using your electric mixer until soft peaks form.
While continuing to mix, pour in the sweetened condensed milk in a steady stream until fully incorporated and the mixture reaches hard peaks.
Add the lemon zest and fold it into the cream mixture gently until fully incorporated.
Layer the bottom of a 9-inch by 13-inch dish (I like using glass baking dishes for icebox cakes) with butter cookies.
Add another layer of butter cookies, then cream, then blueberries.
Add one more layer of each and then top with some more lemon zest.
Chill in the fridge for 6 hours or overnight before slicing and serving (for best results, chill overnight).