Preheat the oven to 350F. Line an 8 by 8-inch baking pan with 2 sheets of parchment paper so it hangs over all 4 sides.
Whisk together the melted butter, granulated sugar, and brown sugar in a large bowl. Whisk in the egg, vanilla extract, and vanilla bean paste. Add the flour and salt, and whisk to combine. Stir in 5 tablespoons sprinkles and the white chocolate.
Transfer the batter to the prepared baking pan and sprinkle the remaining 1 tablespoon sprinkles on top. Bake until the blondies puff up and are light golden along the outside, about 25 minutes, being careful not to overbake.
Let the blondies cool completely in the pan before removing and cutting.
Store leftover blondies in an airtight container at room temperature for up to 5 days.