Step 1

Preheat oven to 350°F. Beat butter with both sugars, baking powder, baking soda, and salt on medium-high speed until light and creamy, 2 to 3 minutes. Beat in vanilla.

Step 2

Add eggs, one at a time, beating to combine after each addition and scraping down sides of bowl as needed. Stop beating and add flour, then beat on low to combine. Add both chocolates and beat to combine. (If you are working in a warm room and/or dough feels sticky or soft, refrigerate about 15 minutes before scooping and baking.)

Step 3

Using a 2-ounce (1/4-cup) scoop, drop dough onto parchment-lined baking sheets, 2 inches apart (6 cookies per sheet); press each down to flatten slightly.

Step 4

Top each cookie with a few large, flat pieces of chopped chocolate or whole féves (if desired). Bake one sheet of cookies 9 minutes; remove from oven and bang sheet on stove top or counter to deflate. Return to oven and bake 3 minutes; remove and bang again, then return to oven and bake until golden around edges and just barely set in centers, about 3 minutes more.

Step 5

Transfer sheet to a wire rack and let cool 5 minutes, then transfer cookies to a rack with a spatula; let cool completely. Repeat with remaining sheets, one at a time. Cookies can be stored in an airtight container at room temperature up to 3 days, or frozen up to 2 months.