Combine unsalted butter, confectioners' sugar, cookie butter, and vanilla in a bowl, using an electric mixer on medium low. Use a small scoop to form 1-inch balls; roll with your hands to smooth; and place on a parchment-lined baking sheet. Melt semi-sweet chocolate chips. Dip each ball into the chocolate with a fork, letting excess drip off. Place balls back on baking sheet, sprinkle with crushed Speculoos cookies, and chill until firm. Store in fridge.