In a stand mixer, cream butter with a paddle attachment.
Scrap down sides and add confectioners' sugar a cup at a time, mixing between cups and scraping down.
Once all of the sugar is added, beat on medium-high speed for 2-3 minutes.
Add cocoa powder, vanilla extract, and salt and beat on low until fully incorporated.
Keep mixer going on low speed while slowly pouring in the heavy cream.
Once heavy cream is fully incorporated, turn off and scrape down the sides of the bowl.
Turn mixer on medium-high speed and beat for 3 minutes until buttercream is light and fluffy.
Gently spread about 1/4 cup of frosting between each layer of cake, stacking nice and straight as you go. Then gently frost the whole cake with a light crumb coat and let set for 20 minutes, you can also place it in the fridge.
Add final layer of frosting to the cake for a finished look. Top cake with Milk Chocolate Hershey's Kisses and gently press sprinkles into the side of the bottom of the cake.