Preheat oven to 350°F (175°C). Grease and flour two 9-inch cake pans. In a bowl, whisk together flour, baking powder, and salt. In a separate large bowl, cream butter and sugar for 3 minutes until fluffy.
Beat in eggs one at a time. Mix in lemon zest, lemon juice, and vanilla. Alternate adding the flour mixture and buttermilk, stirring just until blended. Divide batter evenly into pans.
Bake for 25–30 minutes, until a toothpick comes out clean. Cool in pans for 10 minutes, then transfer to wire racks to cool completely.
Beat cream cheese and butter until smooth. Slowly add powdered sugar, mixing on low, then beat on medium-high until fluffy. Stir in lemon juice, lemon zest, and vanilla. Chill for 10–15 minutes if too soft.
Mix crushed cookies, melted butter, brown sugar, and lemon zest in a bowl. Spread on a baking sheet and bake at 350°F (175°C) for 5–7 minutes until golden. Let cool completely.
Place one cake layer on a serving plate and spread with frosting. Add the second layer and frost the top and sides evenly. Press cooled crunch topping onto the top of the cake.
Melt white chocolate chips with heavy