Preheat oven to 350°. Line a 9-in. square baking pan with parchment, letting ends extend up sides. Combine 1 cup cracker crumbs, 1/3 cup melted butter and 3 tablespoons brown sugar; press onto bottom of prepared pan. Bake 10 minutes. Cool on a wire rack., For blondie layer, in a large bowl, cream softened butter and 1 cup sugar until light and fluffy, 5-7 minutes. Beat in eggs, egg white, and lime juice and zest. In a small bowl, mix flour and 1/2 teaspoon salt; gradually add to creamed mixture, mixing well., Spread over crust. Bake until a toothpick inserted in center comes out clean, 25-30 minutes (do not overbake). Cool completely in pan on a wire rack., For streusel, combine the remaining 1/3 cup cracker crumbs, 2 tablespoons melted butter, 1/4 cup brown sugar, 1 tablespoon sugar and 1/8 teaspoon salt, along with the vanilla and cinnamon, until crumbly. Reserve 1/2 cup for topping., In a large bowl, combine the 5 frosting ingredients; beat until smooth. Stir in remaining 1/2 cup streusel. Spread over bars. Sprinkle with reserved topping. Refrigerate at least 4 hours before cutting. Lifting with the parchment, remove from pan. Cut into bars. Store in an airtight container in the refrigerator. If desired, garnish with sliced Key limes.