Preheat the oven to 350℉. Line 2 large baking sheets with parchment paper.
In a large bowl using a handheld electric mixer, beat the butter, brown sugar, and vanilla on medium speed for 1 minute until fluffy. Add the flour and salt and mix on low until combined.
Dissolve the baking soda in the boiling water and add to the other ingredients in the bowl. Beat again on low until mixed before adding the oats followed by the chopped pecans and chocolate chips.
Scoop the cookie dough by rounded teaspoonful onto the prepared baking sheets, placing 8 cookies per pan, and bake in the preheated oven for 15-17 minutes or until the bottoms are golden brown.
Let the cookies cool for 10 minutes on the baking sheets before gently transferring them to a wire rack to finish cooling. Bake the remaining cookies.
To assemble the sandwiches:
Take the ice cream out of the freezer about 10 minutes before you start assembling to allow it to thaw slightly to be easier to work with. Once the ice cream has slightly thawed, add into the bowl of an electric stand mixer fitted with the paddle attachment and turn the mixer on low the mix the ice cream until smooth and easy to spread onto the cookies.
Sandwich about ⅓ cup of ice cream between two cooled cookies for each sandwich. Work quickly, placing the completed sandwiches on a cold baking sheet lined with wax paper. Place the sheet in the freezer and freeze for about 6 hours or overnight. Dip sandwiches in melted chocolate if desired. Enjoy!