- Preheat oven to 350°.
- Lightly spoon flour into a dry measuring cup; level with a knife. Combine flour, soda, and salt; set aside.
- Melt butter in a large saucepan over medium heat. Remove from heat; stir in cocoa powder and sugars (mixture will resemble coarse sand).
- Add yogurt and vanilla, stirring to combine. Add flour mixture, stirring until moist.
- Drop by level tablespoons 2 inches apart onto baking sheets coated with cooking spray.
- Bake at 350° for 8 to 10 minutes or until almost set.
- Cool on pans 2 to 3 minutes or until firm. Remove cookies from pans; cool on wire racks.