Chill your tools. Place your mixing bowl and beaters in the fridge or freezer for 10 minutes. Cold tools help the cream whip faster and fluffier.

Whip the cream. Add the cold heavy cream to the chilled bowl. Beat on medium-high until soft peaks form. Sprinkle in 2–3 tablespoons of the powdered sugar and whip just to firm peaks. Don’t overbeat.

Make the creamy base. In a separate bowl, whisk the sour cream (or Greek yogurt), remaining powdered sugar, vanilla, lemon juice, and a pinch of salt until smooth.

Fold together. Gently fold the whipped cream into the sour cream mixture until fully combined and fluffy. Folding keeps the mixture airy.

Prep the bananas. Slice the bananas about 1/4-inch thick. Toss lightly with a splash of lemon juice to slow browning. Pat dry if they seem wet.

Add the mix-ins. Fold in the banana slices and mini marshmallows. If using pineapple, nuts, coconut, or cookie pieces, fold them in now. Keep the motion gentle so you don’t deflate the cream.

Taste and adjust. Check for sweetness and tang. Add a touch more powdered sugar or lemon juice if needed. A tiny pinch of salt can sharpen flavors.

Chill to set. Cover and refrigerate for at least 1 hour before serving. This helps the flavors blend and the marshmallows soften slightly.

Serve. Spoon into a serving bowl or individual cups. Top with extra banana slices, crushed cookies, or a light dusting of cinnamon right before serving.