In a small bowl, combine cereal (with marshmallows removed), milk, cream, and salt. Allow to set at room temperature for 30 minutes, stirring occasionally.

In a medium saucepan, combine the cereal milk, vanilla bean paste, and salt. In a small heatproof bowl, combine egg yolks, cornstarch, and sugar.

Cook cereal milk mixture over medium heat until it reaches a gentle boil, stirring often. Gradually pour about one cup of the hot cereal milk mixture into the egg mixture while whisking constantly. Pour the tempered egg mixture into the saucepan.

Continue to cook pastry cream over medium heat, stirring constantly, until it just starts to boil. Remove from heat and whisk until cooled slightly. Beat in the butter until incorporated. Refrigerate until completely cooled.

Preheat oven to 325?F. Grease six 4 inch tartlet pans and set aside.

In a medium bowl, combine the dry ingredients (flour, milk powder, baking soda, salt, and sprinkles).

In the bowl of a stand mixer, combine melted butter, sugar, and brown sugar. Mix well. Add egg and vanilla bean paste, and mix until light and creamy, about 2-3 minutes.

Add the dry ingredients and gently mix with a spatula until just incorporated. Divide the dough among the prepared tartlet pans, pressing it into the bottom and up the sides of each pan.

Place the tartlet pans on a baking sheet and bake for about 20 minutes, until set and slightly golden. Let crusts cool completely in the pans.

To make whipped cream, place cold heavy cream, powdered sugar, and vanilla bean paste in a stand mixer bowl. Start on low speed, then increase to high and whip until thickened and peaks form.

Divide the chilled pastry cream among the cooled blondie crusts, smoothing the tops. Top with whipped cream and sprinkle with Lucky Charms marshmallows if desired.