Pre-heat your oven to 370℉/180℃. Line a 12 hole muffin pan with muffin liners.
In a large mixing bowl combine the white sugar and light brown sugar.
In a small saucepan, heat the unsalted butter and white chocolate over a low heat, stirring frequently until melted. Pour into the mixing bowl with the sugars and whisk to combine everything.
Whisk in the eggs and vanilla until combined. Fold in the flour and chai spice.
Either use an ice cream scoop, or pour the blondie batter into a jug/pitcher to pour into the lined muffin cases. Pour all batter out, ensuring the muffin cases are filled to about 2/3rds (almost full).
Bake 20-23 minutes. Remove from the oven and while still warm, use a tablespoon measure or the end of a wooden spoon to create 'indents' in the Blondie Cups - don't break through the bottom or push to far to the sides - the goal is to create a little dent that can be filled with the frosting.