Preheat the oven to 350°F (180C). Line two baking sheets with parchment paper or silicone silpats.
Measure out ¼ cup of the dark chocolate chips and set aside.
Add the Real California butter and sugar to the bowl of a stand mixer. Using the paddle attachment on medium speed, cream the Real California butter until the sugar has been absorbed and the texture is light and fluffy. Add the California Prune puree and continue mixing on low speed until incorporated, scraping down the sides of the bowl and paddle as needed. Add the egg and vanilla bean paste, then mix until incorporated.
In a small bowl, whisk together the flour, baking soda, and salt. Add the flour mixture to the mixer bowl, mixing on low just enough to incorporate. Add the oats to the mixer bowl and mix on low until everything is evenly distributed. Use a spatula or wooden spoon to fold in the chopped California Prunes and the remaining ½ cup of dark chocolate chips.
With a small cookie scoop, a spoon, or just your hands, form the dough into balls, using 2 tablespoons of the dough per cookie. Then, arrange them on the prepared baking sheets a few inches apart.
Press the dough down with the bottom of a drinking glass greased with baking spray to create a more uniform look among the cookies. The batter won’t spread much as it bakes, which is fine if you are simply making the cookies, but if you are making the Frozen Yogurt Cookie Sandwiches, it is important to flatten them out so that they are all uniform in size and shape. If the cookie dough sticks to the bottom of the glass, use a thin knife or bench scraper to separate it.
Place a few of the ¼ cup of reserved dark chocolate chunks on top of each cookie and press in gently. Bake for 12 minutes, until cooked through and starting to brown around the edges.
To make uniform-sized cookies, when the cookies are done baking, remove the pan from the oven and place it on a work surface. Working one at a time, place a round cookie cutter, slightly larger than the cookie, around a cookie directly on the baking sheet and move the cookie cutter around in a circular pattern. When the cookie's edges are smooth and perfectly rounded, repeat this step with the remaining cookies.
Allow to cool for 10 minutes on the pan then carefully transfer to a wire cooling rack to cool the rest of the way.
These cookies will keep at room temperature, tightly covered for up to 3 days.