Preheat the oven to 350℉. Spray a mini muffin pan (24 mini muffin cups) with nonstick cooking spray. Set aside.
In a small mixing bowl, whisk together the all-purpose flour, graham cracker crumbs, baking soda, and salt. Set aside.
1¼ cup all-purpose flour, 1 cup graham cracker crumbs, ½ teaspoon baking soda, ¼ teaspoon salt
In a separate larger bowl, using an electric hand mixer or the paddle attachment on a stand mixer, beat the butter, brown sugar, and sugar until combined well and fluffy looking; about 1-2 minutes.
1/2 cup (1 stick) butter, 1/2 cup light brown sugar, 1/3 cup granulated sugar
Add in the egg and vanilla extract, and continue beating until combined.
1 large egg, 1 teaspoon vanilla extract
Dump the dry ingredients into the bowl of wet ingredients, mix on low speed just until combined and no flour streaks remain in the dough.* The dough will be somewhat crumbly but should come together when pressed with your fingers. Scoop the dough into the mini muffin tins. Fill them full and press down on the dough to even out the top.
Bake for 8 minutes. They will look slightly underdone and that's perfect.
Immediately after baking, take a teaspoon size measuring spoon and press it into the center of each mini muffin cup, making an indent for the marshmallow to sit in.
Place a half of a marshmallow into each indent, sticky side down, pressing it lightly into the indent.
12 large marshmallows
Let cool for 15 minutes at room temperature.
Place one square of milk chocolate on top of each marshmallow.
2 bars (1.55 oz each) Hershey's milk chocolate
Turn the broiler to high. Place the mini muffin pan in the oven and broil for 1-2 minutes. Watch carefully as they can toast/burn fast!
Let cool for about 5-10 minutes. Eat right away for a warm, gooey treat (my family prefers this) or let them cool and eat at room temperature.