Preheat the oven to 350°F (175°C). Position a rack in the center of the oven and line a baking sheet with a Silpat or parchment paper.

In a large bowl or in the bowl of a stand mixer, place 3/4 cup unsalted butter (room temperature), 3/4 cup light or dark brown sugar, and 1/4 cup sugar. Beat on medium-high for 3–5 minutes until the mixture is light and fluffy.

Add 1 large egg (room temperature) and 2 teaspoons vanilla extract to the butter-sugar mixture. Beat on medium speed for about 1 minute, until fully combined.

In a separate bowl, stir together 1 cup all-purpose flour, 2 cups old-fashioned oats, 1/2 teaspoon baking soda, 1/2 teaspoon kosher salt, and 1 teaspoon ground cinnamon until evenly mixed.

Gradually add the dry ingredients to the wet ingredients and mix on low speed (or stir by hand) until just combined. Do not overmix.

Fold in 1 cup raisins, dried cherries, or cranberries until evenly distributed.

Using a 1-tablespoon scoop or spoon, drop rounded tablespoons of dough onto the prepared baking sheet, spacing cookies about 2 inches apart.

Bake on the center rack for 12–14 minutes for chewier cookies, or 15–17 minutes for crisper cookies, until the edges are set and lightly golden.

Remove the baking sheet from the oven and let the cookies cool on the sheet for 5 minutes. Transfer cookies to a wire rack to cool completely.