How to Make It
In a saucepan, boil the orange juice until it's reduced to 1/3 cup, about 12 minutes. Let cool.
In a microwave-safe bowl, whisk the egg yolks with the sugar. Whisk in the reduced orange juice and stir in the butter. Microwave the mixture on high power for 1 minute, until thickened. Whisk until smooth. Press a piece of plastic wrap directly onto the curd and refrigerate until chilled.
Line a rimmed baking sheet with parchment paper. In a microwave-safe bowl, combine the white chocolate with the oil. Microwave for 1 minute, until the chocolate is just melted; whisk until smooth. Let cool.
Dry the grapes with a towel and set them in a large bowl. Pour in the chocolate, folding to coat. Sift the confectioners' sugar on top and stir until the grapes separate; transfer to the baking sheet and refrigerate for 10 minutes, until the chocolate sets. Serve the grapes in glasses with the orange curd in ramekins alongside.