Preheat your oven to 350°F (175°C). Line a 12-cup muffin tin with paper liners.

In a large mixing bowl, whisk together the flour, granulated sugar, cocoa powder, baking soda, baking powder, and salt.

Add the eggs, milk, vegetable oil, and vanilla extract to the dry ingredients. Beat with an electric mixer on medium speed until just combined, about 1-2 minutes. Scrape down the sides of the bowl as needed.

Carefully pour the boiling water into the batter and mix on low speed until fully incorporated. The batter will be thin, this is normal.

Divide the batter evenly among the 12 cupcake liners, filling each about 2/3 full.

Bake for 18-20 minutes, or until a wooden skewer inserted into the center of a cupcake comes out clean. Let the cupcakes cool in the muffin tin for 5 minutes, then transfer them to a wire rack to cool completely.

In a small saucepan, combine the diced strawberries, 2 tablespoons granulated sugar, and lemon juice. Cook over medium heat, stirring occasionally, until the strawberries soften and release their juices, about 5-7 minutes.

In a tiny bowl, whisk together the cornstarch and 1 tablespoon water to create a slurry. Pour the slurry into the simmering strawberry mixture and stir constantly until the filling thickens, about 1-2 minutes. Remove from heat and transfer to a small bowl. Let cool completely before using.

In a large mixing bowl, beat the softened butter with an electric mixer on medium-high speed until light and fluffy, about 2-3 minutes.

Gradually add the sifted powdered sugar and cocoa powder, mixing on low speed until combined, then increase to medium-high and beat until smooth.

Add the milk (or cream), vanilla extract, and salt. Beat on high speed for another 2-3 minutes until the frosting is light, fluffy, and well combined. If the frosting is too thick, add more milk, 1 teaspoon at a time. If too thin, add more powdered sugar.

Once the cupcakes are completely cool, use an apple corer or a small knife to carefully scoop out a small hole from the center of each cupcake. Don't go all the way through.

Fill each cupcake cavity with about 1-2 teaspoons of the cooled strawberry filling.

Transfer the chocolate buttercream frosting to a piping bag fitted with your desired tip (a large star tip works well for a decorative swirl). Pipe a generous amount of frosting onto each cupcake.

For the chocolate-dipped strawberries: In a small microwave-safe bowl, combine the semi-sweet chocolate chips (and coconut oil, if using). Microwave in 30-second intervals, stirring well after each, until the chocolate is smooth and melted.

Hold a clean, dry whole strawberry by the stem and dip it halfway into the melted chocolate. Gently twist and lift, allowing any excess chocolate to drip off. Place the dipped strawberries on a parchment-lined plate or cooling rack to set. You can refrigerate them briefly to speed up setting.

Once the chocolate on the strawberries is set, carefully place one chocolate-dipped strawberry on top of each frosted cupcake. Serve immediately or store as directed.