1. Prepare a 9x9 pan by lining it with aluminum foil and spraying the foil with nonstick cooking spray. Coarsely chop the jelly beans with a large knife--this is a little difficult, so don't worry if they don't all get chopped up evenly.
2. Place the butter, sour cream, salt, and sugar in a heavy-bottomed medium saucepan over medium-high heat. Stir until the sugar and butter melt.
3. Continue to cook the fudge, stirring frequently, until it comes to a boil. Once boiling, cook it for five minutes, stirring constantly to prevent scorching. If you are using a candy thermometer instead of timing it, it should be at 235 degrees.
4. After five minutes, remove the pan from the heat and add the white chocolate chips and the marshmallow cream. Stir vigorously until the chips and cream are melted and incorporated. If necessary, return the fudge to the heat for brief periods to melt the chips.
5. Add the vanilla and stir well, then add most of the jelly beans, reserving 1/4 cup. Pour the fudge into the prepared pan and smooth it into an even layer. Sprinkle the reserved 1/4 cup of jelly beans over the top, pressing them into the fudge so they adhere.
6. Allow the Jelly Bean Fudge to set at room temperature for 3-4 hours, or in the refrigerator for 1-2 hours. To serve, cut it into small 1-inch pieces. Store Jelly Bean Fudge in an airtight container at room temperature for up to one week or in the refrigerator for up to two weeks.