Chop the bittersweet chocolate into small pieces and place into a large heatproof bowl. Set aside.
Put the heavy cream into a small pan over med-low heat and stir occasionally with a spoon. When it scalds-small bubbles come from the sides, take the pan from the heat and mix in the peppermint extract. Pour the mixture over the chopped chocolate. Let the cream soften the chocolate for almost a minute without stirring. Then stir the mixture with a spoon or spatula starting from the center until all the chocolate melts. Cover the bowl with a plastic film. When it is cool enough, keep in the fridge for 1,5 to hours. If you are in a hurry, you can fasten this process by placing the mixture into a shallow pan.
Take the ganache from the bowl with a small cookie scoop (2 teaspoons) which is 14 grams and roll into balls. Keep in the fridge for 15-20 minutes.
Melt the white chocolate: Place the chopped white chocolate into a heat proof bowl that sits over a pan of simmering water. Stir often.
When the chocolate melts, take the balls from the fridge. Using a fork or a dipping tool, dip the balls one by one into the melted chocolate. Let the excess chocolate drip off by gently tapping the fork on the side of the bowl. Place the balls on a baking sheet covered with parchment paper. Keep in the fridge until ready to serve.