Peanut Butter Shortbread with Salted Chocolate

INGREDIENTS

3/4 cup

unsalted butter, softened

1/2 cup

creamy peanut butter

1/2 cup

brown sugar, packed

1/4 tsp

vanilla extract

2 1/4 cups

unbleached all-purpose flour

1/4 tsp

salt

4 oz

good quality chocolate- milk, semi-sweet, or bittersweet

2 tbsp

unsalted butter, plus additional butter (or shortening) if needed to thin chocolate

Fleur de Sel, for sprinkling