Position a rack in the middle of the oven. Preheat the oven to 350°F. Line 12 muffin tin cups with paper cupcake liners.

Make the cupcakes:
Put the chocolate in a heatproof bowl or the top of a double boiler and place it over, but not touching, a saucepan of barely simmering water or the bottom of the double boiler. Stir until the chocolate is melted and smooth. Remove from the water and set aside to cool slightly.

Sift the flour, baking powder, baking soda, and salt into a medium bowl and set aside.

In a large bowl, using an electric mixer on medium speed, beat the butter and sugar until blended, about 2 minutes. On low speed, mix in the melted chocolate. On medium speed, add eggs one at a time, mixing until each is blended. Add vanilla and beat about 1 minute. Mix in the sour cream until no white streaks remain. On low speed, add half of the flour mixture, mixing to incorporate it. Mix in the water. Mix in the remaining flour mixture until it is incorporated and the batter looks smooth.

Fill each paper liner with 1/3 cup of batter, to about 1/8 inch below the top of the liner. Bake just until the top feels firm and a toothpick inserted in the center comes out clean, about 20 minutes. Cool the cupcakes for 10 minutes in the pan on a wire rack. Remove the cupcakes from the pan onto a wire rack and let cool completely.

Make the filling:
Put the sugar, water, egg whites, and cream of tartar in heatproof container or the top of a double boiler with at least a 2-quart capacity and beat with a handheld electric mixer on high speed about 1 minute. Put the bowl over, but not touching, a saucepan of barely simmering water or the bottom of the double boiler. Beat on high speed until the mixture forms a stiff peak that stands straight up if you stop the beaters and lift them out of the mixture, about 12 minutes (be sure to keep the cord of the mixer away from the burner). The frosting should register 160°F on a thermometer. Remove the container from the water, add the vanilla and almond extracts, and continue beating for 2 minutes to further thicken the filling. The filling will become firmer as it cools on the finished cupcakes.

Spoon the filling into a large pastry bag fitted with a large plain pastry tip or a large plastic freezer bag with a 1/2-inch-long hole cut in one corner. Leaving a is-inch plain edge on each cupcake, pipe a spiral of filling into a 2-inch-high cone-shaped mound on top of each one, using about 1/2 cup of filling per cupcake. Place the filled cupcakes on a platter and refrigerate, uncovered, while you prepare the coating.

Make the chocolate coating:
Put the chocolate and oil in a heatproof bowl or the top of a double boiler and place it over, but not touching, a saucepan of barely simmering water or the bottom of the double boiler. Stir until the chocolate is melted and smooth. Scrape the chocolate coating into a small bowl and cool slightly, about 15 minutes.

Holding each cupcake by its bottom, dip the mound of filling in the chocolate coating, letting any excess drip off, then spoon more coating over the unfilled edge of the cupcake and over the rest of the filling to coat completely. Let sit for 15 minutes.

Return the cupcakes to the platter, refrigerate for about 30 minutes to set the coating, then cover and refrigerate for at least 2 hours. Serve cold.