In a mixer bowl with the paddle attachment, cream together the 1 cup of softened butter, brown sugar and vanilla extract. Add the eggs, one at a time, and mix until fully incorporated.
In a separate bowl, whisk together the gluten-free flour, baking soda, and salt. Next, add the old-fashioned oats and whisk until combined.
Add the dry ingredients to the creamed mixture and mix until you can no longer see any streaks of flour. Do not over-mix.
In a greased jelly roll pan, press 3 cups of the oatmeal mixture into the pan. Press it out evenly. This is a great job for kids!
Fudge Layer
In a heavy saucepan, over low heat, melt together the sweetened condensed milk, chocolate chips, butter, and salt. Once melted remove the saucepan from heat and stir in the vanilla.
Pour the fudge mixture over the pressed oatmeal. Spread it out evenly, like frosting.
Dot the remaining oatmeal mixture over the fudge layer. Use a heaping tablespoon for each dot. Use up all remaining oatmeal mixture.
Bake in a 350 degrees F heated oven for 20-25 minutes. The top will be golden brown and sink into the fudge.
Let cool before cutting, if you can. It will be easier to cut but hard to resist!
Notes
Gluten-Free Flour: If you do not need to use gluten-free flour, all-purpose flour will work with no quantity changes.Old-Fashioned Oats: Be sure your oats are certified gluten-free if you are making these for someone who cannot have cross-contamination with gluten. On the low FODMAP diet, cross-contamination with wheat will not make me sick, so using standard old-fashioned oats is just fine.