Preheat the oven to 350 degrees F (175 degrees C).

Grease a 9x13-inch baking pan.

In a medium bowl, combine 1 cup tahini, 3/4 cup Greek yogurt, 1/2 cup white sugar, 1 egg, and 2 tablespoons milk.

Mix the tahini topping ingredients until smooth.

In a separate bowl, combine 1 cup melted unsalted butter and 1 1/4 cups white sugar.

Mix the butter and sugar until well combined.

Whisk in 3 eggs one at a time, beating well after each addition.

In another bowl, combine 1 1/4 cups all-purpose flour, 3/4 cup unsweetened cocoa powder, 1/2 teaspoon ground cinnamon, 1/2 teaspoon baking powder, and 1/4 teaspoon salt.

Gently mix the dry ingredients into the butter mixture until the batter is thick and smooth.

Remove 1 cup of the brownie batter and set aside.

Spread the remaining batter into the prepared baking pan.

Pour the tahini mixture on top of the brownie batter.

Spread the tahini mixture all the way to the edges of the pan.

Drop small teaspoonfuls of the reserved brownie batter evenly over the tahini mixture.

Gently swirl a knife through the tahini layer to create a marbled effect.

Bake in the preheated oven until a skewer inserted in the center comes out almost clean, about 35 to 40 minutes.

Remove the brownies from the oven and cool completely before slicing into squares.