Step 1: Preheat your oven to 350°F (175°C) and line two large baking sheets with parchment paper.
Step 2: Prepare the streusel topping by combining the 1/2 cup flour, 1/2 cup brown sugar, and 2 teaspoons cinnamon in a small bowl. Stir in the melted butter until crumbly.
Step 3: In a large mixing bowl, cream the softened butter with the granulated and brown sugars until light and fluffy.
Step 4: Add the eggs one at a time, beating well after each addition, then mix in the vanilla extract.
Step 5: Whisk together the 3 cups flour, baking powder, baking soda, salt, and 1 tablespoon cinnamon in a separate bowl.
Step 6: Gradually blend the dry ingredients into the wet mixture, then fold in any optional nuts or chocolate chips.
Step 7: Scoop the dough into 1.5-inch balls and place them on the baking sheets. Press a tablespoon of streusel firmly into the top of each ball.
Step 8: Bake for 10-12 minutes until the edges are set and golden. Cool on the pan for 5 minutes before moving to a wire rack.