Crush 1 cup cereal into fine bits with some small crunchy pieces; set aside. For the streusel, crush the remaining ½ cup into coarse crumbs, toss with 2 tbsp sugar and ¼ cup melted butter, and set aside.

Preheat oven to 350°F (175°C). Line two baking sheets with parchment. Cream ½ cup softened butter, ½ cup granulated sugar, and brown sugar on medium speed until fluffy, about 2 minutes, then beat in egg and vanilla.

Whisk flour, baking soda, baking powder, and salt in a bowl. On low speed, add dry ingredients to butter mixture in two batches until just combined. Fold in the finely crushed cereal by hand.

Scoop dough into 2-tablespoon balls, place 2 inches apart on sheets. Press about 1 teaspoon streusel firmly onto each dough ball.

Bake one sheet at a time for 10 to 12 minutes, until edges are golden and centers look slightly underdone. Cool on the sheet 5 minutes, then transfer to a wire rack.