Pre-heat oven: 180°C / 160°C (fan) / Gas 4 / 350°F
In a heatproof bowl, melt the white chocolate, sugars and butter (microwave for 45-60secs, 20secs at a time), stirring until smooth.
In a large bowl, beat the egg and vanilla together until lightly foamy, then pour into the melted white chocolate mix and beat together until fully combined.
Toss your chocolate chips in the flour before sieving the flour into the chocolate mix and folding in gently. Stir in the flour-coated white chocolate chips until spread throughout.
Line an 8inch square tin with greaseproof paper and pour half of the mix into the pan, smoothing evenly.
Microwave the Biscoff spread for 15secs and then spread this evenly across the blondie mix, leaving an inch/few cm border at the edges.
Sprinkle your crushed Biscoff biscuits over the spread then cover this with the remaining blondie mix, gently smoothing across to fully cover the Biscoff below.
Gently press 8 Biscoff biscuits into the top of your blondies, spaced evenly.
Bake for 25-30mins until your blondie only has a slight wobble in the centre. It will harden further as it cools.
Once cooled, remove from the tin. Heat more Biscoff spread in the microwave to drizzle over the top for an optional extra touch before cutting into squares.