Step 1

Preheat oven to 325°F. Lightly coat a 10-inch cast-iron skillet with cooking spray. Beat brown sugar, granulated sugar, and butter with a heavy-duty electric stand mixer at medium speed until light and fluffy. Add egg, milk, and vanilla, beating until blended.

Step 2

Whisk together flour, baking soda, and salt in a bowl. Add to butter mixture gradually, beating at low speed until combined.

Step 3

Add 1 cup of the chocolate chips; beat until combined.

Step 4

Spread mixture evenly in prepared skillet. Top with remaining 1/2 cup chocolate chips.

Step 5

Bake in preheated oven until golden and set, about 50 minutes. Let stand 15 minutes; cut into wedges. Serve with vanilla ice cream.

Step 6

Pecan Praline: Omit chocolate chips. Prepare recipe as directed, stirring in 1/2 cup chopped pecans and 1/2 cup toffee bits in Step 3 and topping mixture with 3/4 cup pecan halves and 3 tablespoons jarred caramel sauce in Step Sprinkle with sea salt just before serving.

Step 7

Mississippi Mud: Increase milk to 5 tablespoons. Prepare recipe as directed, whisking 3 tablespoons unsweetened cocoa into flour mixture in Step 2 and topping cookie with 1/4 cup miniature marshmallows during the last 30 minutes of baking in Step

Step 8

Strawberry Shortcake: Increase milk to 1/4 cup. Substitute white chocolate chips for semisweet chocolate chips. Prepare recipe as directed, beating 3/4 cup chopped frozen pound cake into mixture with white chocolate chips in Step Top mixture with 1/4 cup chopped frozen pound cake in Step Serve cookie wedges with whipped cream and sliced strawberries.

Step 9

Grasshopper: Omit milk and chocolate chips. Prepare recipe as directed, beating 3 tablespoons bourbon into mixture with egg and vanilla in Step 1 and stirring in 1 cup halved thin crème de menthe chocolate mints in Step Top mixture with 1/4 cup halved thin crème de menthe chocolate mints in Step

Step 10

Hummingbird: Omit milk and vanilla extract. Substitute white chocolate chips for semisweet chocolate chips. Prepare recipe as directed, adding 1/4 cup mashed banana and 1 1/2 teaspoons coconut extract to butter mixture in Step 1 and 1/2 cup sweetened flaked coconut and 1/2 cup chopped dried pineapple in Step