Melt white chocolate either in a double boiler (or a heat-proof bowl set securely over a pot of simmering water) or the microwave at intervals and frequent stirring.
While chocolate is melting, cover a baking sheet in parchment paper. Sprinkle Oreo cookies and pretzel twists on parchment-lined baking sheet.
Pour white chocolate over Oreo cookies and pretzels. Spread with offset spatula if needed.
Top with M&Ms, conversation hearts, and sprinkles.
Let Valentine's Day bark harden in fridge for about 2 hours before breaking into pieces and enjoying.