In a mixing bowl, combine cornstarch, egg yolks, and a splash of milk, whisking until smooth. In a saucepan, heat the remaining milk with sugar and cinnamon over medium heat until just below boiling. Gradually whisk in the cornstarch mixture, continuing to stir until the pudding thickens. Remove from heat, cover, and let it cool completely before transferring to the refrigerator to chill overnight.

Preheat your oven to 175 °C (350 °F) and line a muffin tin with cupcake liners. In a large mixing bowl, beat room temperature unsalted butter, sugar, and vanilla extract until fluffy. Incorporate eggs one at a time, mixing well after each addition. In a separate bowl, sift together flour and baking powder, then fold them into the butter mixture along with the fragrant cinnamon, ensuring everything is well combined.

Spoon the cupcake batter into the prepared muffin liners, filling each about two-thirds full. Place the muffin tin in the preheated oven and bake for 15-20 minutes, or until a toothpick inserted into the center of a cupcake comes out clean. Once baked, remove the pan from the oven and allow the cupcakes to cool in the tin for a few minutes before transferring them to a wire rack to cool completely.

After the pudding has chilled overnight, whip it until fluffy and smooth. In a separate bowl, mix mascarpone cheese and cream cheese until perfectly blended. Gently fold the whipped pudding into the mascarpone mixture, creating a creamy and decadent topping for your Cinnamon Cupcakes.

Once the Cinnamon Cupcakes are completely cool, pipe the mascarpone mixture generously onto each cupcake. For an added crunch and visual appeal, sprinkle cinnamon sugar over the tops and garnish with Cini Minis.