Heat the oven to 350 degrees. Spray a quarter sheet pan with non-stick cooking spray and line with parchment paper.

On low speed, pour in the buttermilk, oil and vanilla, raise the speed to medium-high and beat for 6 minutes. Scrape down the sides.

On low speed, add the flour, baking powder, salt and 1/4 cup of  the rainbow sprinkles. Mix just till the batter comes together, about a minute more.  Scrape down the sides.

Use an angled spatula to spread the cake batter in an even layer in the pan. Sprinkle the remaining 2 tablespoons of rainbow sprinkles evenly on top.

Bake the cake for 30 to 35 minutes, or till set in the center and no longer jiggly. Cool in the pan on a wire rack. The cooled cake can be wrapped in plastic wrap and stored in the fridge for up to 5 days or frozen for up to one month.

Heat the oven to 300 degrees. Line a sheet pan with parchment paper.

Beat the sugars, flour, baking powder, salt and sprinkles on low speed till well combined.

Transfer the crumbs to a food processor and process until the consistency of sand. Store in an airtight container for up to one month in the freezer.

Whisk the milk and vanilla in a small bowl or measuring cup.

Combine the cake scraps and vanilla milk in a medium sized bowl and toss with your hands until moist enough to knead into a ball. If needed, you can add up to 2 tablespoons more milk.

Line a sheet pan with parchment paper.

Use a small ice cream scoop to scoop out the cake onto your baking sheet. Use your hands to roll each scoop into a smooth ball.

Melt the white chocolate in the top half of a double boiler set over barely simmering water. Remove from heat and whisk in the oil until smooth and emulsified.

Place the birthday cake sand into a medium bowl.

Working with one ball at a time, use a fork to dip into the melted chocolate. Rap the handle of the fork against the rim of the bowl so that any excess chocolate drips off. Gently drop the ball into the sand and use another fork to toss the sand over the ball, coating it evenly. You can use your hands to re-roll if you like. Return to the baking sheet and repeat with the remaining ingredients..

Refrigerate for 5 minutes to set the chocolate before serving. The truffles can be stored in an airtight container in the fridge for up to 1 week, or in the freezer for up to a month.