Line an 8x8 inch (20x20 cm) square baking pan with parchment paper, allowing an overhang on two sides. This will help with lifting the bars out later.

In a food processor, finely crush the Biscoff cookies until they resemble fine crumbs. Alternatively, place cookies in a sturdy Ziploc bag and crush with a rolling pin.

Transfer the cookie crumbs to a medium bowl. Pour in the melted unsalted butter and mix well until the crumbs are evenly moistened.

Press the mixture firmly and evenly into the bottom of the prepared 8x8 inch pan. Use the back of a spoon or a flat-bottomed glass to compact it well. Place the pan in the refrigerator to chill while you prepare the filling.

In a large mixing bowl, using an electric hand mixer or stand mixer with the whisk attachment, beat the cold heavy cream on medium-high speed until stiff peaks form. Be careful not to overbeat. Set aside in the refrigerator.

In a separate large mixing bowl, beat the softened full-fat cream cheese on medium speed until completely smooth and creamy, about 2-3 minutes. Scrape down the sides of the bowl as needed.

Add the sifted powdered sugar, slightly melted Biscoff cookie butter spread, and vanilla extract to the cream cheese mixture. Beat on low speed until just combined, then increase to medium and beat until smooth and well incorporated, ensuring no lumps.

Gently fold about one-third of the whipped cream into the cream cheese mixture using a rubber spatula to lighten it. Then, carefully fold in the remaining whipped cream until no streaks remain and the mixture is light and airy. Be careful not to deflate the whipped cream.

Remove the chilled cookie crust from the refrigerator. Spoon the cheesecake filling over the crust and spread it evenly with an offset spatula or the back of a spoon, creating a smooth top.

Cover the pan loosely with plastic wrap and refrigerate for at least 4 hours, or preferably overnight, until the cheesecake is completely set.

Once the cheesecake is firmly set, carefully lift it out of the pan using the parchment paper overhang. Transfer it to a cutting board.

Gently warm the remaining 60g Biscoff cookie butter spread in the microwave for 15-30 seconds until it's pourable. Drizzle it evenly over the top of the chilled cheesecake. If desired, sprinkle with extra crushed Biscoff cookies for garnish.

Allow the topping to set for 5-10 minutes at room temperature, or briefly chill again. Using a sharp knife wiped clean between cuts, slice the cheesecake into 9 equal bars. Serve immediately or store in the refrigerator.