Step 1

Preheat the oven to 325°F with a rack in the middle. Grease an 8" square pan or line it with a parchment sling.

Step 2

, To make the sugar cookie dough : Weigh your flour; or measure it by gently spooning it into a cup, then sweeping off any excess. In a medium bowl, whisk the flour, baking soda, and salt until well-combined.

Step 3

, In a large bowl or the bowl of a stand mixer fitted with the flat beater attachment, beat the butter on low speed until smooth, about 2 minutes. Scrape down the sides of the bowl, add the sugars, and beat on low speed until well-combined but not necessarily fluffy, about 2 minutes. Scrape down the sides of the bowl, add the egg and extracts, and beat until well-combined, about 1 minute. Add the sour cream and beat to fully incorporate, another 30 seconds. Add the flour mixture and pulse the mixer to incorporate it slowly until just combined.

Step 4

, Transfer half of the sugar cookie dough (about 390g) to a medium bowl and set aside. Add the cocoa to the remaining dough in the mixer and beat just until combined (finish by hand with a spatula if any dry spots remain).

Step 5

, Use damp hands or a cookie scoop to dollop the chocolate dough all over the bottom of the prepared pan. Use damp hands to press it into an even layer.

Step 6

, Dollop the reserved vanilla dough all over the top of the chocolate dough, again using damp hands to press it into an even layer. For the neatest surface, use an offset spatula or the straight side of a bowl scraper to smooth out the surface.

Step 7

, Bake the sugar cookie bars for 35 to 40 minutes, until the surface is barely golden brown and a paring knife or toothpick inserted into the center comes out clean. Transfer the pan to a wire rack until cool enough to handle. Remove bars from the pan and allow to cool completely.

Step 8

, To make the raspberry topping : Place the raspberries in a fine mesh strainer set over a medium bowl. Use a flexible spatula or the back of a spoon to smash and press the berries through the strainer to get as much juice as possible. Discard the solids or reserve them for another use.

Step 9

, Gradually mix in 1 cup (113g) of the confectioners’ sugar, stirring until smooth. Slowly add the additional 1/4 cup (27g) confectioners’ sugar as needed until you reach a thick but pourable consistency (thicker than maple syrup but thinner than honey). Whisk in the vanilla and salt.

Step 10

, Pour the glaze over the cooled bars and spread it all the way to the edges; an offset spatula is a helpful tool here. (For the most even coating, use a spoon to drizzle glaze on areas that have risen near the edges of the pan before glazing the center.) Top the sugar cookie bars with sprinkles, if desired. Set aside to allow the glaze to set.

Step 11

, Once glaze has set, slice the sugar cookie bars into pieces. We like cutting these bars into 24 small slices using a 6 x 4 pattern.

Step 12

, Storage instructions : Store sugar cookie bars well-wrapped at room temperature for up to 4 days. Freeze unglazed bars for up to 6 months. Thaw before topping.