Preheat the oven to 350 ℉. Grease and flour 2 (8-inch cake pans). In a medium bowl, combine the lemon zest and the sugar with your fingers until the sugar is moist and fragrant. Set aside. In a large stand mixer fitted with the paddle attachment, cream together the butter and coconut oil. Add the sugar and mix until light and fluffy.
Add the eggs and sour cream and mix just until combined. In a separate medium bowl, whisk together the flour, baking powder, and salt. Add ⅓ of the flour mixture along with ⅓ of the milk and lemon juice to the wet ingredients. Mix on low speed just until combined. Repeat with another ⅓ of the flour mixture and the remaining milk and lemon juice.
Fold in the remaining flour and blueberries just until combined. Pour into prepared cake pans and bake for about 30 minutes or until a toothpick inserted into the center comes out clean. Remove from the oven and let the cakes cool most of the way on a wire rack. Use a butter knife to go around the edges of the pan and loosen the cake.
Invert the cakes carefully onto a wire rack to cool completely. *If making the cakes ahead of time, wrap the cakes in plastic wrap while they are still warm and freeze. this will ensure the cake stays moist. Let the cake come to room temperature before frosting.
Make the frosting. In a stand mixer fitted with the whisk attachment, beat the cream cheese for a few seconds. Add the vanilla, salt and powdered sugar and beat until smooth. Add the heavy cream and beat on medium-high speed until very stiff peaks form, scraping down the bowl occasionally.
Frost the cake and decorate with lemon slices, clusters of blueberries and mint leaves for a fun summer touch. Store the cake in an airtight container in the fridge for up to 4 days.