The pole, who also plies his trade in the Blancpain GT Series, lapped the Kent venue’s full GP layout in 1m27.379s to end up 1.244s faster than top Iron Cup contender and AF Corse driver Martin Lanting aboard a GTE-spec 458.
Broniszewski set his benchmark time with half the session remaining to extend his grip at the top of the times. That was just before Lanting usurped Nicolas Vandierendonck for second after the Selleslagh Racing-run Corvette had spent much of the opening 20 minutes as Broniszewski’s closest rival.
Patrick Van Glabeke’s AF Corse Ferrari was less than a tenth shy of the C6 ZR1, while Alexis de Bernardi completed the top-five.
Jan Brunstedt had given Lanting a run for his money in the Iron Cup standings for much of the session but slipped to sixth in the final classification, albeit just ahead of Misano Qualifying Race podium finisher Anthony Pons and former Le Mans class winner Karim Ojjeh.
Ferrari pair Leon Price and Stephen Earle completed the top-10.
However, it was a surprise to see championship leader and Misano Main Race winner Mario Cordoni down in 17th, 6.7s slower than Broniszewski’s quickest time.
Qualifying for tomorrow morning’s first race takes place at 15:50 BST this afternoon.