1 Place a walnut half on the top of each brownie. 2  Bake in a 325º oven for about 20 minutes or until brownies look dry and feel firm to the touch. 3  I do these in my convection oven and it takes about 15 minutes. 4  Let cool in pans for about 10 minutes then transfer to wire rack to cool completely.irections. 1  In a medium-size pan, place butter and chocolate and heat over low heat. 2  Remove pan from heat and stir in sugar and vanilla. 3  Add eggs, one at a time, stirring well after each addition. 4  Stir in flour. 5  Spoon batter into mini muffin pan sprayed with cooking spray, filling almost to the top. 6  Place a walnut half on the top of each brownie. 7  B