Melt the butter and mix with yogurt in a large bowl.
1/2 cup butter, 1/2 cup plain greek yogurt
Add the sugar and beat with a hand mixer.
1 cup granulated sugar, 1 cup brown sugar
Add in one egg at a time, beating well after each addition.
4 eggs
Stir in the vanilla.
1 T vanilla
In a medium bowl, whisk together the cocoa, flour, and salt. Add to the wet ingredients and use a spatula to mix together. Smooth the top and set aside.
1.5 cups all-purpose flour, 1 cup cocoa powder, 1 t salt
Cook Sauce
In a small saucepan over medium heat, combine the strawberries, sugar, and 1 T balsamic vinegar.
1.5 cups chopped strawberries, 1 T sugar, 2 T balsamic vinegar
Bring to a simmer and cook, while smashing down the strawberries with a spatula.
When the mixture has reduced a little, remove from heat and stir in the second T of balsamic vinegar.
Add spoonfuls of strawberry mixture over the brownie mixture and swirl it in. The strawberry mixture should mostly remain on the top, so don't mix too much!
Bake & Serve
Sprinkle the chocolate chips over the top and place in oven.
1/4 cup semisweet chocolate chips
Bake for 30-45 minutes or until toothpick comes out clean (make sure you aren't poking through a chocolate chip or it might not look clean!).