Leave the eggs out and let the butter soften at room temperature before preparing the recipe. If you need to speed up the softening, unwrap the stick of butter and microwave it in a bowl in 20-second intervals on low until softened.
Preheat the oven to 350℉/177℃. Line a large baking sheet with parchment paper or a silicone mat and set aside. If you want to bake both batches at the same time, line two sheets.
In a large mixing bowl, cream the softened butter and brown sugar with an electric hand mixer until light and fluffy.
Add the eggs, one at a time, and vanilla extract. Mix until combined.
In a separate bowl or measuring cup, combine the whole wheat flour, baking powder, cinnamon, and salt. Add this mixture to the bowl with the wet ingredients. Use a rubber spatula to stir until just combined.
Fold in the oats, roughly chopped cranberries, and chopped walnuts with a rubber spatula.
Scoop out a heaping tablespoon of batter, ideally with a small 1 tablespoon cookie scoop. If you don't have a cookie scoop, wet your hands first so that the batter doesn't stick to them and roll the scooped batter into a ball. Place it on the prepared baking sheet. Repeat until you fill the baking sheet with balls placed 2 inches apart from one another. Use your palm to gently flatten each ball until it's about ½-inch thick.
Bake on the center rack of the preheated oven for 10 to 13 minutes until lightly browned around the edges. To keep them as chewy as possible, don't overbake. Remove the baking sheet from the oven. Let them cool for a few minutes on the sheet then promptly transfer to a cooling rack.
Repeat the process with the rest of the batter. Alternatively, you can bake two baking sheets at a time. Rotate the trays halfway through cooking time.
Enjoy the cookies warm or after cooling!
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