In a medium bowl, combine raisins and warm water. Let them soak for 30 minutes.

After 30 minutes, drain the raisins well and pat them dry with paper towels. Set aside.

Preheat the oven to 350°F (175°C). Line a 9x13-inch baking dish with parchment paper, leaving some overhang on the sides for easy lifting.

Add the softened butter, brown sugar, and granulated sugar to the bowl of a stand mixer fitted with the paddle attachment. Cream together on medium speed until light and fluffy, about 2–3 minutes. Scrape down the sides of the bowl as needed.

Add the eggs and vanilla. Mix on medium speed until fully combined and smooth.

In a separate large bowl, whisk together oats, flour, cinnamon, baking soda, and kosher salt until evenly combined.

With the mixer on low speed, gradually add the dry ingredients to the wet mixture, mixing until just combined. Do not overmix.

Gently fold in the raisins until evenly distributed throughout the batter.

Spread the batter evenly into the prepared pan and smooth out the top.

Bake for 35-40 minutes, or until the edges are golden brown and a toothpick inserted in the center comes out with a few moist crumbs but no raw batter.

Let the bars cool completely in the pan before frosting.

While the bars cool, prepare the frosting. To the bowl of a stand mixer with the paddle attachment (or using a hand mixer), add the cream cheese, butter, and vanilla extract. Mix on medium speed for 1–2 minutes, or until smooth and fully combined.

Add the confectioners’ sugar one cup at a time, mixing on low after each addition, until the frosting is smooth and creamy.

Spread the frosting evenly over the cooled bars using an offset spatula. Slice and serve.