Note: The cookie butter can be found next to the nut butters in well-stocked grocery stores, including Trader Joe’s. Make the Speculoos Squares: Position a rack in the middle of the oven and preheat to 325°F. Grease a 9 × 13-inch metal baking pan with the nonstick pan spray. Line with parchment paper, leaving some overhang on the long sides so it’s easy to lift out after baking. Lightly coat the paper with pan spray. lace the cookie butter and butter in a large, microwave-safe bowl and microwave in 30-second increments, stirring between each, until completely melted, 60 to 90 seconds total. Add the brown sugar and whisk until smooth. Add the eggs and vanilla extract and whisk until smooth and ribbony. Add the flour, baking powder, baking soda, salt, and ¼ teaspoon of the cinnamon. Stir with a rubber spatula just until a soft dough forms with no pockets of dry flour. Transfer the dough to the prepared baking pan and press into an even layer using clean hands coated with pan spray. Combine the granulated sugar and sprinkle over the top. Lightly press the sugar into the dough with your hands. Bake until the top is lightly browned and the edges are set and a toothpick inserted into the center comes out clean, 30 to 35 minutes. Let cool at room temperature for at least 2 hours. As the bars cool, make the glaze: In a medium bowl, whisk together the confectioners’ sugar and milk until smooth. Transfer half the glaze (about 1½ tablespoons) to a second medium bowl and add the cookie butter and cinnamon. Whisk until completely smooth, adding additional milk to thin it as needed. Both glazes should be thick yet pourable. If either of them is too thick, add additional milk; if too thin, add additional confectioners’ sugar. Drizzle the top of the bars with the glazes and let set for 20 minutes, then slice into 24 pieces (6 long rows by 4 short rows). Storage: The bars will keep in an airtight container at room temperature for up to 1 week.