Peel and cut the bananas in half lengthwise.
In a skillet large enough to accommodate them, heat about a tablespoon of butter or ghee over medium-high heat and cook the bananas cut-side down for a few minutes, until golden on the bottom.
Gently flip with a thin spatula and cook until golden on the other side. Transfer to a plate to cool.
In a large bowl, beat the mascarpone or cream cheese, sugar and vanilla until creamy and lump-free.
Add the whipping cream and beat until stiff peaks form.
Put the coffee (and a shot of rum or Kahlúa, if you like) into a shallow bowl and dunk the ladyfingers as you layer them into the bottom of a dish or glass or arrange them on a platter.
Add a layer of sautéed bananas, and spread with about half the cream mixture.
Add another layer of dunked ladyfingers, another of bananas, and cover with the remaining cream.
Use a fine sieve to dust the top with cocoa powder.