Step 1

1 Preheat the oven to 350 degrees

Step 2

2 Use some butter to generously grease a 9-by-13-inch deep-sided baking pan

Step 3

3 (See VARIATION, below

Step 4

4 )

Step 5

5 Combine the butter and sugar in the bowl of a stand mixer or handheld electric mixer; beat on high speed for about 3 minutes, until fluffy and homogenous

Step 6

6 Stop to scrape down the bowl

Step 7

7 Add the eggs, oil and vanilla extract; beat on medium-low speed for about 1 minute or until just combined

Step 8

8 Stop to scrape down the bowl

Step 9

9 Add the flour, salt and baking soda, beat on medium-low speed until just combined, for about 30 seconds, then add the milk and beat for about 30 seconds, to form a soft dough

Step 10

10 Spread the dough evenly in the pan, making sure it gets into the corners

Step 11

11 Scatter the decorative sprinkles on top with a generous hand, using even more if you want particularly colorful cookies, or sprinkle with cinnamon sugar

Step 12

12 Bake (middle rack) for 20 to 25 minutes, until the cookie slab has puffed, lightly browned and become firm to the touch

Step 13

13 (This will result in a slightly underbaked-in-the-center cookie

Step 14

14 If you prefer it firmer, bake for another 3 to 5 minutes

Step 15

15 )

Step 16

16 Cool completely in the pan before cutting into squares

Step 17

17 VARIATION: The baked cookie slab is heavy and quite moist at the center, so if you'd rather not cut these squares while they're in the pan, first line the pan with a parchment paper that's long enough to hang over the short sides

Step 18

18 (Grease the pan as well

Step 19

19 )