Oil for greasing the pot liner
For the crust:
2 cups graham cracker crumbs (from about 18 graham crackers)
½ cup melted unsalted butter
1/3 cup granulated sugar
For the brownies:
1/2 cup unsalted butter
8 ounces semisweet chocolate, chopped
1 cup granulated sugar
Three large eggs
1 1/4 cups all-purpose flour
1/4 cup unsweetened cocoa powder
3/4 teaspoon baking powder
1/2 teaspoon salt
For the topping:
Four (1.55-ounce) Hersheys milk chocolate bars (or 4 ½ ounces milk chocolate), broken into sections
1 (10-ounce) bag mini marshmallows
Line a slow cooker with greased parchment paper or with a silicone liner.
To make the crust, in medium bowl, combine the cracker crumbs, melted butter, and sugar and stir to mix well. Press the mixture into the prepared slow cooker pot in an even layer that covers the whole bottom of the pot.
Mix and melt the chocolate and butter over a double boiler, or a bowl placed over a saucepan with boiling water, stirring continuously. Once the mixture is melted and well combined, remove the pot from the heat. Add the sugar and stir to mix. Add the eggs, one at a time, mixing after each addition until incorporated. Finally, add the flour, cocoa powder, baking powder, and salt, and stir to mix.
Pour the batter into the slow cooker on top of the crust, and spread it into an even layer.
Arrange the milk chocolate pieces on top of the batter. Cover and cook on low for 2 ½ hours.
Remove the lid and sprinkle the marshmallows over the top. Cover the pot again and cook, on low, for about 10 minutes longer, until the marshmallows are melted. Remove the inner pot from the slow cooker and set it on a rack to cool.
