Grind speculoos cookies to a fine powder using a food processor.

Add confectioner's sugar to the ground cookies and mix well.

In a separate bowl, combine egg yolk, milk, and softened butter.

Add the wet ingredients to the dry ingredients and mix until smooth.

Transfer the mixture to a closed plastic container with a lid.

Refrigerate for 2 hours to allow the mixture to firm up.

Shape the chilled mixture into small balls using your hands.

Refrigerate the shaped truffles for 15 minutes to firm up further.

Melt the white chocolate in a double boiler or microwave, stirring frequently.

Grind the remaining speculoos cookies into a fine powder.

Dip each truffle into the melted white chocolate, ensuring it's fully coated.

Immediately roll the chocolate-covered truffle in the ground speculoos cookies.

Place the coated truffles on a sheet of parchment paper.

Allow the truffles to set completely in the refrigerator.

Keep refrigerated until serving time.