Pre-heat your oven to 370℉/180℃. Line an 8″ Square Pan with greaseproof paper.
In a small bowl, break up the white chocolate and melt in the microwave in 20 second intervals, stirring in between to make sure it doesn’t burn.
In a large mixing bowl, whisk together the melted butter and both sugars for 3-5 minutes. Add in the eggs and vanilla extract and mix again.
Whisk in the melted white chocolate until fully incorporated. Fold in flour and chai spice blend. Pour into lined tin and bake 25-30 minutes (if it's still just a little wobbly, that's fine). Let cool.