Position a rack in the center of the oven and preheat to 325°F.
Cream 1 cup sugar the butter in the bowl of a stand mixer fitted with paddle attachment. (You can use a hand mixer if you allow the butter to soften at room temperature before starting.) Paddle on low speed, then medium, for a total of 2-3 minutes. Add the eggs all at once and paddle at low speed until blended, about 1 minute. Add the syrup and paddle for another minute; the mixture will be very wet, but that’s okay. Paddle on low speed for about 1 minute then stop and scrape. Add the flour, paddle on low for 1 minute, then scrape. Paddle on low until thoroughly mixed; the mixture will still be very wet and look a little grainy.
Spray by 13x9x2” baking tray with nonstick spray and line the bottom with parchment paper. Pour the batter into the pan. In won’t even come halfway up the sides—that’s all right.
Bake until crispy on top, the batter begins to pull away from the sides of the pan and a toothpick inserted to the center comes out clean, about 30 minutes.
Remove the tray from the oven and let the brownies cool in the pan. Cover a cutting board with parchment paper. Sprinkle the brownies with the remaining 1 tablespoon sugar and gently turn the brownies out onto the parchment paper by inverting the tray. Peel off the parchment if it is stuck to the brownies.
For the icing, put the sugar, butter and milk in a pot and bring to a boil, stirring, over medium-high heat.
Remove the pot from the heat and whisk in the chocolate until melted.
Let the mixture cool slightly then ice the brownies using an offset spatula while the icing is soft and pliable. Use right away; do not let it stiffen and do not store.
Cut the brownies into 6 even strips (1 1/2-inches each) along the length of the batch then crosswise at 3 1/4-inch intervals to make 24 brownies.Note
: The brownies should be enjoyed as soon as possible, but can be refrigerated in an airtight container for up to 3 days. They may also be frozen for up to 1 month. Let them come up to room temperature before serving.