Preheat oven to 350°F. Line a muffin tin with 12 cupcake liners.

Place 2 1/4 teaspoon lemon juice in a measuring cup. Add enough milk to the measuring cup to equal 3/4 cup; let sit for a few minutes.

In a medium-sized mixing bowl, whisk together the flour, baking soda, spices, and salt; set aside.

In a stand mixer fitted with the paddle attachment, beat the butter and both sugars together until combined. Add in the egg, egg yolk, and vanilla. Mix on high until light and fluffy, about 1-2 minutes. Stir in the pumpkin puree and remaining 1 and 1/2 teaspoons lemon juice.

With mixer on low, alternate adding the dry ingredients with the milk mixture until just combined. Do not overmix. Pour/scoop batter into cupcake liners, then bake for 18-22 minutes, or until a toothpick inserted in the center comes out with few crumbs attached. Allow cupcakes to cool for 15 minutes before transferring to a wire rack to cool completely.

Place the chocolate in a medium bowl. Combine heavy cream and butter in a small saucepan, stirring over medium heat until mixture is smooth and just begins to simmer. Pour over the chocolate, cover with plastic wrap, and allow to sit for 2-3 minutes. Remove wrap, and stir until smooth. Refrigerate until it reaches a thicker pudding-like consistency.

Add the egg whites and sugar to a large heatproof bowl and set over a saucepan of barely simmering water. Heat mixture, stirring constantly, until the temperature hits 160ºF on a candy thermometer, about 3-5 minutes. Remove bowl from saucepan, add the cream of tartar, and beat mixture with an electric hand-mixer (or in a stand mixer) on high speed until stiff glossy peaks form, about 6-8 minutes. Add the vanilla near the very end.

Using a sharp knife, carve a hole into the center of each cupcake, about halfway deep. Remove cake piece and fill hole with chocolate ganache. Pipe/Spread frosting on top of the cupcake. Toast the frosting with a kitchen torch, then top with a Hershey bar segment and graham cracker piece.