Preheat the oven to 350°F (180°C). Grease and line a square baking pan.
In a bowl, whisk together the flour, cocoa powder, baking powder, and salt.
In another bowl, mix the melted butter and granulated sugar until well combined.
Add the plain yogurt, milk, and vanilla extract to the wet ingredients and mix.
Gradually add the dry ingredients to the wet ingredients, mixing until just combined.
In a small bowl, dissolve the instant coffee granules in hot water.
Dip the sponge fingers into the coffee mixture and place a layer of them in the bottom of the prepared pan.
Pour the brownie batter over the layer of sponge fingers.
Bake in the preheated oven for 25-30 minutes or until a toothpick inserted in the center comes out with a few moist crumbs.
Allow the brownies to cool completely in the pan.
In a bowl, whip the heavy cream with powdered sugar and vanilla extract until stiff peaks form.
Spread the whipped cream over the cooled brownies.
Dust the top with cocoa powder before slicing and serving.
