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. Alternatively do this using a double boiler: Place the chocolate in a heat proof bowl resting on a small saucepan with simmering water. Stir until melted.
In a large mixing bowl, whisk together the melted butter and both sugars. Add in the eggs and vanilla extract and mix again.
Whisk in the melted white chocolate until fully incorporated. Add the flour and fold to combine.
Pour half the mixture into the pan, add on the jam and spread about. Pour over the remaining blondie batter. Bake 25-30 minutes.
Remove and let cool, then make the glaze. Combine the icing sugar and milk and stir. Add a little more milk if needed, until you reach a pourable but not thin consistency. Add the sprinkles and let set before slicing and serving!