Place butter, powdered sugar, salt, and flour, in a food processor. Pulse until the mixture resembles a coarse meal.
Add the egg whites and process just until a uniform dough is obtained. If the dough is not coming together, add a little water (1-2 teaspoons).
Shape the dough into a disk about 1 inch thick before chilling. Wrap the dough in plastic wrap and transfer it to the refrigerator for 1 to 2 hours (up to overnight).
Roll the dough on a floured surface to a ¼ -inch (½ cm) thickness and cut circles using a cookie cutter. Place a flat teaspoon of the chocolate spread and 2-3 mini marshmallows in the center of each circle.
Arrange the Hamantaschen on a baking sheet lined with parchment paper.
Place the baking sheet in the freezer for 30 minutes to an hour before baking.
Preheat the oven to 350°F/180°C.
Bake for 15-20 minutes until the Hamantaschen is slightly golden. Let them cool.
Place the chocolate in a microwave-safe bowl. Microwave for 30 seconds intervals, mixing in between, until completely melted and smooth. Stir in the oil.
Partly dip each Hamantaschen into the chocolate. Place on parchment paper and sprinkle Graham crackers on top. Let it set and enjoy!