1. Prepare ingredients: Mix rice krispies and fruity pebbles in a large bowl. Pre-measure jumbo marshmallows and mini marshmallows in separate bowls.

2. Line pan: Line your square pan with parchment paper on all sides, leaving overhang for easy removal.

3. Melt butter: Place butter in nonstick pot over low to medium heat. Once melted, reduce to low heat.

4. Add marshmallows: Add jumbo marshmallows and vanilla extract. Stir continuously with rubber spatula until mostly melted and well combined (3-5 minutes). Remove from heat if mixture gets too hot.

5. Add cereal: Remove pot from stovetop. Add cereal mixture and fold together until completely coated, scraping edges and bottom of pot.

6. Add mini marshmallows: Pour in mini marshmallows and stir until evenly dispersed but not completely melted.

7. Press into pan: Transfer mixture to lined pan. Use spatula (or buttered measuring cup) to press evenly into corners and across entire pan.

8. Cool: Refrigerate for 15 minutes or let sit at room temperature for 30-45 minutes.

9. Make drizzle: Melt white chocolate in microwave (10-15 second intervals, stirring between) or on stovetop. Crush 1 tablespoon fruity pebbles in plastic bag until sandy. Mix into melted white chocolate.

10. Cut and decorate: Remove treats from pan using parchment overhang. Cut into 16 squares with sharp knife. Transfer white chocolate mixture to piping bag or plastic bag with small corner cut. Drizzle over treats.

11. Set and serve: Let drizzle set at room temperature or in fridge. Store in airtight container at room temperature for up to 3-4 days.