Shokoladnaya Kartoshka (Russian Chocolate Cake Truffles)

Using a food processor, grind the cookies or cake scraps into very fine crumbs (you're looking for a sand-like texture). Transfer the crumbs to a medium bowl and set aside.
Add the sweetened condensed milk and butter to a small saucepan over medium-low heat and heat until the butter has melted completely, then add in the cocoa powder, powdered sugar, and vanilla extract and stir until fully combined and smooth. Turn off the heat.
Pour the chocolate mixture into the crumbs and mix until a chocolate dough starts forming. Work fast to keep the butter from cooling down and becoming too hard.
Divide the dough into 14 portions for 14 round cake truffles or into 6 portions for 6 large potato-shaped truffles. I usually make 14 cake truffles with this recipe (0.8 oz each / 25 g each). Roll them into balls or into the shape of a potato, then place them on a clean plate, cover with plastic wrap and refrigerate for 15 minutes. If the dough is too dry and crumbly, simply add more condensed milk!

Chop the semi-sweet chocolate and place it in a microwave-safe bowl. Melt in the microwave in 30-second intervals stirring after every 30 seconds. Melt until completely smooth then set aside.
Line a baking sheet with parchment paper. Then using a fork or a dipping tool, drop each cake truffle into the melted semi-sweet chocolate, push it under the surface of the chocolate and then lift it out and tap the fork against the side of the bowl to remove the excess chocolate. Finally, place the truffle on the prepared baking sheet. Repeat with the remaining truffles. Immediately add sea salt or sprinkles if desired. Refrigerate for 30 minutes or until the coating has set.
Optional: meanwhile, chop the white chocolate and place it in a microwave-safe bowl. Melt in the microwave in 30-second intervals stirring after every 30 seconds. Melt until completely smooth. Immediately pour the chocolate into a piping bag and cut off the tip (the hole should be tiny). Remove the truffles from the refrigerator and drizzle with your melted chocolate. Return to the refrigerator and chill for another 15 minutes. Allow to come down to almost room temperature before serving.