Prepare the Pan:
Line an 8×8-inch metal baking pan with parchment paper, allowing the paper to hang over the edges for easy removal. Preheat your oven to 375°F (190°C).
Make the Cookie Dough:
In a stand mixer, cream together the butter and sugar for 3 minutes, until light and fluffy.
Mix in the eggs and vanilla extract until just combined. Scrape down the sides of the bowl as needed.
Gradually add the flour, salt, and baking soda, mixing until the dough starts to come together.
Chill the dough in the fridge for 20 minutes to make it easier to handle.
Assemble the Cookie Bars:
Press half of the cookie dough evenly into the bottom of the prepared pan.
Carefully lift the pressed dough out of the pan using the parchment paper and transfer it to a baking sheet. Place in the freezer to firm up.
Replace the parchment in the pan, then press the remaining cookie dough evenly into the pan.
Spread the strawberry preserves over the top of the dough.
Remove the chilled dough from the freezer and place it on top of the preserves, pressing down to secure it.
Bake:
Bake in the preheated oven for 25-28 minutes, or until the top is golden brown.
Let the bars cool completely in the pan on a wire rack.
Flip and Glaze:
Once cooled, use the parchment paper to lift the cookie bars from the pan. Flip the bars upside down so the bottom is now on top.
In a small bowl, whisk together the powdered sugar, milk, and vanilla extract until smooth. Pour the glaze over the top of the bars and decorate with rainbow sprinkles.
Set & Serve:
Let the bars sit at room temperature for 1-2 hours until the glaze sets. Cut into 15 bars and enjoy!