Step 1: Butter a 13 x 9 x 2-inch pan. Line the pan with parchment paper. Make sure the paper hangs over the edge approximately 2 inches on each side.
Step 2: In a large saucepan, melt butter on medium heat. It will melt, bubble, turn clear golden and finally start to turn brown. Keep stirring and scrape any butter bits from the bottom of the pan.
Step 3: Remove pan from heat and mix in the marshmallows until the marshmallows are melted and smooth with the butter. Mix in the salt, rice cereal, and freeze-dried strawberries. Stir until combined.
Step 4: With a buttered spatula, press the rice mixture into the bottom of the pan. Cover the top with the sprinkles. Let sit for 20 minutes. Using the overhanging parchment, pull and place the entire slab of rice treats onto a cutting surface. Cut into 2.5" x 3" rectangles.
Step 5: In a microwave-safe bowl, heat the white chocolate melting wafers in 15-30 second intervals stirring until smooth. Using a butter knife or an offset spatula, decorate the rice treat with a triangle on the 3-inch side to look like a flap of an envelope. Dip the back of the gummy heart in the white chocolate and place at the tip of the white chocolate envelope flap. Let cool and serve the same day with your valentine message.