Preheat your oven to 350°F (175°C). Line an 8x8-inch baking pan with plastic wrap, leaving some overhang each side for easy removal.

In a large mixing bowl, whisk together the unsalted butter and granulated sugar until light and fluffy, about 1 minutes.

Add the large egg and egg yolk, one at a time, beating well after each addition.

Mix in the vanilla extract until combined

Press half of the sugar cookie dough evenly into the prepared baking pan. Take another piece of plastic wrap and place it on top. Evenly press the dough across the pan make sure its an even layer. Carefully, pull the dough out of the pan and place it in the fridge.

Line the same 8x8-inch baking pan with parchment paper, leaving some overhang for easy removal. Use metal binder clips to hold down the sides if needed. Spray the sides and bottom of the pan.

Press the other half of the sugar cookie dough evenly into the prepared baking pan.

Spread the strawberry jam over the dough layer, leaving a small border around the edges.

Take the other half of the cookie dough out of the fridge, by now it should have firmed up a bit and be easier to work with. Gently place it on top of the strawberry jam. Make sure it covers the entire pan.

Bake in the preheated oven for 25-30 minutes, or until the edges are golden brown and a toothpick inserted into the center comes out clean. Allow the blondies to cool completely in the pan on a wire rack.

In a small bowl, whisk together the powdered sugar, 1-2 tablespoons of whole milk, and mix until smooth and pourable. Adjust the consistency with more milk if needed.

Once the blondies are completely cooled, drizzle the glaze over the top.

Decorate with rainbow sprinkles while the glaze is still wet.

Allow the glaze to set before cutting the blondies into squares. Serve and enjoy!