Cream butter and sugar together. Add salt, vanilla, and egg, and beat on medium-high until light, fluffy, and volume has grown, about 3-4 minutes.
Beat in baking soda, flour, flax meal, and walnuts. Batter should be easy to pick up and just barely tacky. Add in cranberries and the various chocolate chips. Mix well. Scoop dough into an airtight container, and let it rest in the fridge overnight (and up to 4 days).
When ready to bake, preheat oven to 375 F / 190 C. Mold cold cookie dough into 1.5-inch cubes, and place on ungreased cookie sheet about 2" apart. Bake for 8 to 9 minutes, until golden around the edges and still a little gooey inside. Let cool on cookie sheet for 3-4 minutes, then transfer to a rack to cool completely.
Keep cookies in an airtight container or, even better, freeze them in zip topped bags. These cookies are great right out of the freezer or thawed.
Notes
An easy vegan egg substitute is flax or chia eggs: 1 Tablespoon of ground flax meal or chia seeds mixed with 3 T warm water. Let it sit for 5 minutes to gel.To make these gluten free, simply substitute the all purpose and whole wheat flours for a one-to-one GF baking flour.