Preheat your oven to 350°F (175°C) and line a muffin tin with cupcake liners.
In a medium saucepan, melt the unsalted butter and semi-sweet chocolate chips over low heat, stirring until smooth. Remove from heat and let it cool slightly.
In a large mixing bowl, whisk together the melted chocolate mixture, coconut or canola oil, granulated sugar, eggs, egg yolk, and vanilla extract until well combined.
In another bowl, sift together the all-purpose flour, baking soda, baking powder, cocoa powder, and salt.
Gradually add the dry ingredients to the wet ingredients, alternating with the sour cream and hot coffee or hot water. Begin and end with the dry ingredients, mixing until just combined.
Spoon about a tablespoon of batter into each cupcake liner. Add a teaspoon of Nutella into the center of each, then top off with more batter until the liners are about two-thirds full.
Bake in the preheated oven for 18-20 minutes or until a toothpick inserted in the center comes out clean. Allow the cupcakes to cool in the pan for 5 minutes before transferring them to a cooling rack.
In a small saucepan, combine the frozen raspberries and lemon juice and cook over medium heat until the raspberries break down and become syrupy. Strain the mixture through a fine sieve to remove the seeds, and let it cool.
In a large mixing bowl, beat the very soft unsalted butter until creamy. Gradually add the sifted confectioners' sugar and salt, mixing until light and fluffy.
Once the raspberry mixture has cooled, mix it into the frosting. Add heavy cream to achieve the desired consistency, and beat until well combined.
Once the cupcakes are completely cooled, frost them generously with the raspberry frosting. You can use a pastry bag for a decorative touch.
Top each cupcake with a fresh raspberry for a pop of color and added flavor.