Place the cream in a small saucepan over medium heat. Heat it until it simmers and small bubbles form all along the edges of the pan, but do not allow it to come to a full boil.
While the cream is heating, prepare the white chocolate and banana mixture. If you have a food processor, place the half banana in the food processor and mix until the banana has liquefied.
Add the white chocolate chips to the banana and process until the white chocolate is in small pieces. The mixture will clump together, so stop the processor several times to scrape it down. Once the cream is simmering, with the processor on, carefully pour the hot cream in a small stream down into the bowl of the processor and let it run until the white chocolate has melted and the ganache is smooth and free of lumps.
If you do not have a food processor, this can be done in a mixer, or you can mash the banana by hand and add very finely chopped white chocolate to it, stirring until well-combined. Pour the hot cream over the white chocolate-banana mixture and whisk it until it is smooth. This method produces a ganache that tastes the same, but there might be small pieces of banana that are not incorporated.
Once everything is smooth, scrape the ganache into a bowl and whisk in the banana extract, if using. Cover the ganache with cling wrap and refrigerate until firm enough to scoop and roll, about 2 hours.
Once the ganache is firm, coat your hands with powdered sugar and roll the ganache into small balls, dusting your hands with more powdered sugar to prevent sticking if necessary.
Keep the balls chilling in the refrigerator while you melt the white candy coating. Once melted, use a fork or dipping tools to dip the truffles into the coating, then set them on a foil-lined baking sheet. Refrigerate the tray to set the white chocolate for 10 minutes.
After all the truffles are dipped, it’s time for the best part: decorating them! For the chocolate “sauce,” melt the chocolate candy coating in a small bowl. In order to get the chocolate to drizzle just right, it needs to be very thin and fluid. If your candy coating is thick, add up to 2 tablespoons of oil, adding a little at a time and stirring and testing after your additions. It should easily flow off the spoon in a thin line.
Using a spoon, place a small spoonful of dark chocolate on top of a truffle, and use the tip of the spoon to nudge it off the sides in a thin stream. Alternately, you can place the candy coating in a bag and cut off the tip and pipe it onto the truffles.
After all of the truffles have their chocolate “sauce,” sprinkle the still-wet chocolate liberally with colored sprinkles. The last step is to add your red candies that represent the cherry. This can be a red M&M, jelly bean, red hot, or any other small red candy. Full-sized M&Ms are a little large for my taste, so I like to cut them in half for my truffles, but it’s definitely not necessary.
Refrigerate the tray to set the chocolate coating. Store Banana Split Truffles in an airtight container in the refrigerator for up to a week. For the best taste and texture, bring them to room temperature before serving.