Oatmeal and Turbinado Cream Cookie Sandwiches

INGREDIENTS

1 1/2 cups

old-fashioned rolled oats (5 1/4 ounces/150 grams)

1 cup

firmly packed dark muscovado sugar (8 ounces/227 grams)

1/2 cup

whole wheat pastry flour, spooned and leveled (4 1/4 ounces/120 grams)

1/2 tsp

fine sea salt

1/2 tsp

baking soda

1/4 tsp

baking powder

1/2 tsp

ground cinnamon

1/4 tsp

freshly grated nutmeg

1/2 cup

cold unsalted butter, cut into cubes (1 stick/4 ounces/113 grams)

large egg yolk

2/3 cup

turbinado sugar (4 5/8 ounces/132 grams)

large egg whites

1/4 tsp

fine sea salt

1/2 cup

butter, cut into 1/2- inch cubes, soft but still cool (1 stick/4 ounces/113 grams)

1 tsp

pure vanilla extract