Wipe the mushrooms clean with a damp cloth. Slice 1/4 inch thick. Set aside.
Heat olive oil in a large skillet and add the onion and garlic. Saute until the onion is softened and the garlic is fragrant, 3-4 minutes.
Add the vinegar, brown sugar, lemon pepper and tarragon. Simmer mixture for a few minutes. Add the mushrooms and continue to cook 7-10 minutes, stirring frequently. The liquid should reduce and thicken slightly.
Put in a glass jar or zip top bag and refrigerate overnight or for up to 3 days. Serve as part of a relish tray, on a salad, or as a side dish.
Heat oven to 350 degrees. Cream butter and sugars together until light and fluffy. Add the eggs and vanilla and beat to combine well.
Dissolve the baking soda in the hot water. Add to egg and sugar mixture and mix. Add the flour and stir until well combined.Stir in the nuts and chocolate chips until evenly combined.
Using a small cookie scoop, place dough on parchment lined baking sheets. about 2 inches apart. Bake for 10 - 12 minutes. Allow to cool on pan for 5 minutes. Transfer to a wire rack to cool completely.
Store airtight for up to 1 week.