Preheat oven to 350F. Prepare 3 cookie pans with parchment paper.

In small bowl, combine oat flour, tapioca flour, baking soda and salt.

In large bowl, beat butter and sugars on medium speed with an electric mixer until smooth, about 3 minutes. Add egg and vanilla to butter mixture and continue to beat 2 minutes until light in color. Gradually add flour mixture, beating slowly while incorporating. When fully combined, fold in 1-1/2 cups chocolate chips.

Using cookie scoop, scoop cookies by heaping tablespoonfuls evenly onto prepared pans, leaving at least 2 in. between each cookie. Top cookies with remaining 3/4 cup chocolate chips, pressing into top and sides to make sure they stick. Chill pans in refrigerator at least 1 hour.

When fully chilled, sprinkle with flaky sea salt, if using, and bake 8-11 minutes or until edges are slightly brown and middle is still soft. Cool on pans 10 minutes, then remove to cooling rack to cool at least 10 minutes longer. Cookies are best served warm.

Cookies may be kept for up to one week in sealed airtight container.