Preheat the oven to 350°F (175°C). Grease and flour a 9-inch round cake pan.
In a large mixing bowl, cream together the butter and sugar until light and fluffy.
Add the peanut butter and mix until well combined.
Beat in the eggs, one at a time, then stir in the vanilla extract.
In a separate bowl, whisk together the flour, cocoa powder, salt, and baking powder.
Gradually add the dry ingredients to the wet ingredients, mixing until just combined.
Pour the batter into the prepared cake pan and smooth the top.
Bake in the preheated oven for 30-35 minutes or until a toothpick inserted into the center comes out clean.
Let the cake cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.
To make the ganache, heat the heavy cream in a saucepan until it just begins to simmer.
Place the chocolate chips in a heatproof bowl and pour the hot cream over the chocolate.
Let it sit for 2 minutes, then stir until smooth and glossy.
Allow the ganache to cool slightly before pouring over the cooled cake.
Spread the ganache evenly over the top of the cake and let it set before slicing and serving.