Adjust oven rack to middle position and preheat the oven to 170C/338F. Line two 12-cup cupcake pans with 16 paper liners.

In a medium bowl, whisk together the flour, cocoa powder, baking soda and salt to combine. Set aside.

In a small bowl or a large liquid measuring cup, whisk together the buttermilk, vinegar, vanilla and food coloring. Set aside.

In the bowl of a stand mixer fitted with the paddle attachment (or in a large mixing bowl and an electric hand mixer), beat the butter on medium speed until creamy, about 1 minute. With the mixer running, gradually add in the sugar, then slowly drizzle the oil. Raise the speed to medium-high and continue beating together, scraping down the bowl as necessary, until lightened up in both color and texture; 4 to 5 minutes. The color should turn very pale (almost white) and texture should look soft and fluffy.

Add the eggs, one at a time, beating well after each addition.

Scrape down the bowl and beater with a spatula, then resume mixing on lowest speed. Add in one-third of the flour mixture and beat until just incorporated. Pour in half of the buttermilk mixture and beat lightly until combined. Repeat with half of the remaining flour mixture, remaining buttermilk mixture, and ending with the remaining flour mixture, scraping down the bowl as necessary. Mix until just combined and a smooth batter forms, being careful not overmix.

With a rubber spatula, give the batter one good, final stir to make sure that everything is well incorporated. Use an ice cream scoop to divide the batter evenly among the 16 cupcake liners, filling them up 3/4 of the way.

Bake until the cupcake's center springs back when lightly touched and a toothpick inserted in the center comes out clean or with a few moist crumbs attached, about 20 minutes. Resist the urge to open the oven's door while the surface is still looking wet, or the cupcakes might risk sinking in the middle.

Let cool in the pan for about 5 minutes then transfer to a wire rack to cool completely before frosting. While the cupcakes bake, make the Whipped Cream Cheese Frosting.

In the bowl of a stand mixer fitted with the whisk attachment (or in a large bowl and an electric handheld mixer), beat the butter until lightened up and creamy; 2 to 3 minutes.

With the mixer running on low speed, gradually add in the confectioners sugar, followed by the salt. Raise the speed to medium-high and whip until lightened in both color and texture; about 5 minutes.

With the mixer still on medium-high speed, add one piece of cream cheese at a time, one after the other, mixing well after each addition so there are no lumps. Continue whipping until light and fluffy, and air pockets have formed.

Beat in the vanilla and sour cream (if using) just until incorporated.

Fill a piping bag fitted with your favorite piping tip (I used Ateco 808 and Ateco 867) with the Whipped Cream Cheese Frosting. To frost, start piping in the center, going around once, then ending with a swift pull.

Top with the chocolate seal stamps (if using), red fondant hearts or sprinkles, if desired. The frosted cupcakes will keep well at room temperature in an airtight container for 24 hours. Please refer to the FAQs for longer storage.

Place the metal wax seal stamp in the cup filled with crushed ice or over an ice pack to thoroughly chill the bottoms.

If you don’t ice your seals, the chocolate will stick to the wax seal.

Grate 12g of the chocolate and set aside. In a small, microwave-safe bowl, microwave the remaining 38g os chocolate in 15 second intervals, stopping and stirring in between until mostly melted. Continue to stir the chocolate until it has completely melted and very smooth. Stir in reserved grated chocolate until fully melted. (This process of melting 3/4 the amount of chocolate first and then adding in the remaining grated 1/4, is a quick way to temper the chocolate, which will allow the toppers to set firmly without melting to the touch; so don't skip it).

 Let the chocolate stand 3-5 minutes or until it's barely warm to the touch. It's important that the chocolate is not too warm when you make an impression with the stamp, or it will stick to the stamp.

Pour the melted chocolate into a piping or zipper lock bag with the end snipped off. Squeeze 3/4-inch round drops of the chocolate onto a parchment lined baking sheet. Make a row of 3 to 4 chocolate drops.

Remove the stamp from the ice and quickly wipe it off of any water droplets with a towel. Place the chilled stamp onto a chocolate round, press down gently, then let stand for 10 seconds or until the chocolate looks set around the edges. Gently lift the stamp and you should now have a chocolate seal. Place back the metal wax stamp into the ice to rechill and repeat with remaining melted chocolate. Refrigerate finished chocolate seals until firm.

Peel firmed seals from the parchment paper and place over the cupcakes.