Making the Chocolate Cupcakes:

1. Preheat the oven to 350°F (175°C) and line a 12-cup muffin tin with cupcake liners. This step ensures that the cupcakes will be easy to remove after baking.

2. Mix the dry ingredients: In a large mixing bowl, whisk together the flour, granulated sugar, cocoa powder, baking powder, baking soda, and salt. This combination of dry ingredients forms the foundation of your cupcake batter.

3. Whisk the wet ingredients: In another bowl, beat the eggs, milk, vegetable oil, and vanilla extract. This will give the cupcakes their richness and moisture.

4. Combine wet and dry ingredients: Gradually add the wet ingredients to the dry ingredients and stir until smooth. The batter should be well combined but still have a slightly thick consistency.

5. Add boiling water: Slowly add the boiling water to the batter and stir until smooth. This step makes the batter thin, but don’t worry—it will result in moist cupcakes.

6. Fill the cupcake liners: Pour the batter into the cupcake liners, filling each about two-thirds of the way full. This ensures that the cupcakes rise without overflowing.

7. Bake the cupcakes: Place the muffin tin in the preheated oven and bake for 18-20 minutes, or until a toothpick inserted into the center of a cupcake comes out clean. Once baked, let the cupcakes cool completely on a wire rack.

Making the Caramel Filling:

1. Prepare the caramel mixture: In a medium saucepan, combine the brown sugar, heavy cream, unsalted butter, and salt. Cook over medium heat, stirring occasionally, until the butter melts and the sugar dissolves.

2. Simmer the caramel: Allow the mixture to simmer for 3-4 minutes, stirring constantly. The caramel should thicken slightly.

3. Add vanilla extract: Once the caramel has thickened, remove the saucepan from heat and stir in the vanilla extract. Allow the caramel to cool to room temperature before using it in the cupcakes.

Making the Caramel Buttercream Frosting:

1. Beat the butter: In a large mixing bowl, beat the softened butter with a hand or stand mixer for about 2 minutes, until it becomes light and fluffy.

2. Add the powdered sugar: Gradually add the powdered sugar, one cup at a time. Beat well after each addition until the frosting is smooth and creamy.

3. Add cream and flavoring: Add the heavy cream, vanilla extract, and a pinch of salt. Mix until the frosting is well-combined and smooth.

4. Stir in the caramel sauce: Gently mix in the cooled caramel sauce to the frosting. If the frosting is too thick, you can add more cream to reach the desired consistency.

Assembling the Cupcakes:

1. Core the cupcakes: Once the cupcakes are cool, use a cupcake corer or a small knife to carefully remove a portion of the cake from the center. This will create a well to fill with caramel.

2. Fill with caramel: Spoon about a tablespoon of the caramel filling into each cupcake, filling the center generously.

3. Frost the cupcakes: Use a piping bag or a spatula to frost each cupcake with the caramel buttercream. Be generous with the frosting to ensure a rich, creamy topping.

4. Add extra caramel drizzle: For an extra touch of sweetness and visual appeal, drizzle some additional caramel sauce over the top of each frosted cupcake.