Use a hand mixer or stand mixer to cream together 3/4 cups brown sugar, 6 Tablespoons softened unsalted butter, and 1/4 teaspoon kosher salt in a large bowl. Add 1/2 teaspoon vanilla extract and mix until incorporated. Add the oat flour and stir until mixed. Mix in 6 Tablespoons mini chocolate chips.
Divide the cookie dough in half (the most accurate way to do this is to use a kitchen scale). Line an 8x8" baking pan with plastic wrap, parchment paper, or wax paper and press half of the cookie dough into the pan evenly. Use your fingers or the flat bottom of a glass to press the cookie dough in, then use an offset spatula to get into the edges. Carefully lift the pressed cookie dough out of the pan and set it aside on a cutting board or another flat surface.
Re-line the pan with plastic wrap, parchment paper, or wax paper, and press the remaining cookie dough into the pan following the same process as above. This time, leave the cookie dough there.
Spread 1 pint softened vanilla ice cream over the layer of cookie dough, smoothing it into the corners with an offset spatula. Carefully lift the first sheet of pressed cookie dough, turn it onto the ice cream, and peel off the plastic wrap/parchment/wax paper. Gently press the cookie dough down into the ice cream.
Cover the baking pan with plastic wrap and transfer to the freezer for at least 2 hours.
Remove the pan from the freezer and turn over onto a large cutting board to remove the ice cream sandwiches (if they remain stuck in the pan, carefully run some warm water over the bottom of the pan, being careful not to get any water on the ice cream sandwiches). Peel off the plastic wrap/parchment/wax paper.
Use a large knife to cut the ice cream sandwiches into your desired size (8 full-size rectangles or 16 small squares work well). Serve immediately, or place the sandwiches in an airtight container or zipper bag and return to the freezer.
Notes
If you happen to have oat flour, you can skip step 1 and use 1 1/2 cups of oat flour instead of rolled oats.