Step 1

Adjust toaster oven or oven rack to middle position and heat oven to 325 degrees. Line small rimmed baking sheet with parchment paper. Whisk flour, baking soda, and salt together in bowl. Using rubber spatula, mash butter and sugar together in separate bowl until well combined and lightened in color. Add egg yolk and vanilla and mix until combined. Stir in flour mixture until just combined then stir in chocolate chips.

Step 2

Divide dough into 2 portions, then roll into balls. Place on prepared sheet, spaced about 2 inches apart. Bake until edges of cookies are set and beginning to brown but centers are still soft and puffy, 8 to 12 minutes. Let cookies cool on sheet for 10 minutes. Serve.