Preheat the oven to 350°F (175°C). Oil a 9- x 13-x 1-inch sheet pan and line it with parchment paper.

Note: For thicker brownies, this recipe can easily be doubled. If doubling, use the same sized pan; the brownies will be about double the thickness.

Whisk, measure and sift together the flour, cocoa powder, sugars, baking powder, salt and baking soda together into a medium bowl.

*Note: If the flour does not contain xanthan or guar gum add 1/4 tsp of either to the flour.

Combine the oil, milk, Prune Puree, maple syrup and extracts in a medium bowl, whisking to thoroughly to blend.

Pour the wet ingredients into the dry ingredients and mix with a silicone spatula until the batter is smooth. It will be thick. Stir the chocolate chips and chopped walnuts into the batter.

Spoon the batter into the prepared pan and evenly spread it out using an offset spatula. The batter might seem like it will not fully cover the pan, but it will. Keep moving it until the bottom of the pan is covered.

Transfer to the preheated oven and bake for 13 to 15 minutes or until the top is set, the brownies have risen and a tester or wooden skewer inserted into the middle has only a few crumbs attached.

Remove from the oven and place the pan on a wire rack to cool to room temperature. When cool, wrap in plastic wrap and freeze before cutting.

Once frozen, cut into squares. Store, airtight, in the freezer. Note, as these brownies defrost, they become somewhat sticky, so they are best eaten straight from the freezer. They do not freeze rock hard, which makes them perfect for turning into delicious ice cream sandwiches. If making ice cream sandwiches, it is best to make the sandwiches and freeze before serving.