To make the oatmeal cookie bars: Preheat the oven to 350°F with a rack in the center. Line an 8" square pan with a parchment sling and lightly grease.

In a medium bowl, whisk together the brown sugar, butter, and molasses until well combined. (A dough whisk is a helpful tool here.)

Add the egg and vanilla and whisk until well combined.

Add the flour, oats, cinnamon, baking powder, and salt; switch to a flexible spatula and mix until combined and no dry streaks remain.

Add the raisins; stir until well distributed.

Transfer the mixture to the prepared pan and spread it into an even layer. (A small offset spatula is a helpful tool here.)

Bake the oatmeal cookie bars for 25 to 30 minutes, or until evenly browned, set in the center, or a digital thermometer inserted into the center reads 205°F.

Remove the bars from the oven. Let them cool slightly in the pan before using the parchment to transfer them to a wire rack to cool completely. (The bars can be made 2 days in advance; store airtight at room temperature.)

To make the glaze: In a medium bowl, whisk together the confectioners’ sugar and 2 teaspoons water to form a thick, shiny mixture. Add additional water, if needed, in 1/2-teaspoon increments until the mixture resembles the consistency of honey and easily drizzles off the whisk.

Drizzle or pipe the glaze onto the bars. Allow the glaze to set briefly (about 5 to 10 minutes) before slicing.

Storage information: Store leftover oatmeal cookie bars airtight at room temperature for up to 3 days. Freeze for longer storage.