Preheat the oven to 350°F. Line a square 8 x 8 baking pan with parchment paper.
Whisk the flour, graham cracker crumbs, baking powder, and salt together in a medium bowl to combine and set aside.
In a large bowl, add melted butter and both sugars and whisk to combine. Whisk in the vanilla and then the eggs, blending and whisking eggs vigorously until well combined.
Stir in the flour mixture into the butter mixture, mixing just until blended. Fold in ¼ cup white chocolate chips.
Spread about ¾ of the batter into the prepared pan in and even layer. Spread the guava marmalade evenly over the batter. Dollop the marshmallow crème evenly over the top, then spoon the rest of the batter into pan. Using an offset spatula or knife gently swirl the guava and fluff into the batter. Sprinkle the remaining ¼ cup white chocolate chips on top and finish with the cookie pieces all over batter
Transfer the pan to the oven and bake for 20 to 25 minutes, or until a toothpick inserted in the center comes out clean. Carefully pull the cake with the parchment out of the pan and allow it to cool completely (if you cool in the pan the residual heat will continue to bake the cake and will dry out).
Cut into 18 small bars. Enjoy!
