Preheat the oven to 350 °F (175 °C) and line an 8"×8" (20cmx20cm) pan with parchment paper.
In a medium mixing bowl, stir together the flour, cocoa powder, and salt. Set aside.
1 cup (125 grams) flour, 3/4 cup (86 grams) Dutch-process cocoa powder, 1/4 teaspoon salt
In a large mixing bowl, stir together the fat, sugar, and vanilla extract. Once combined, add the yogurt, and stir just until combined.
2/3 cup (150 grams) butter or refined coconut oil, 1 1/2 cups (300 grams) granulated sugar, 1 tablespoon vanilla extract, 3/4 cup (182 grams) full-fat plain Greek yogurt
Add the dry mixture to the wet and stir just until almost no streaks of flour remain. Do not overmix!
Fold in chocolate chips. It's okay if it kind of forms a big, slightly greasy ball of batter. Just make sure that the oil/butter is incorporated and not floating at the top.
3/4 cup (128 grams) semi-sweet chocolate chips
Transfer the batter into the prepared pan, use a silicone spatula or spoon to even it out, and sprinkle the mini chocolate chips on top, if using.
1/4 cup mini semi-sweet chocolate chips
Bake for 20-24 minutes or until the middle is no longer jiggly. The toothpick test won't work here. Let them cool completely before cutting. They are very gooey. I would recommend chilling them for a bit to help them firm up.
Store in an airtight container for up to 3 days at room temperature, refrigerated for 1 week, or frozen for up to 3 months.