In a separate bowl, combine all the ingredients and mix with a spoon or your hand to make the streusel. Start with \cutext{1/3}{cup} (\cunum{43}{g}) of flour. The mixture should stick together, but should also crumble when you run it through your fingers. If it isn't crumbling, add \cunum{1}{EL} additions of flour until it crumbles.
Using a large (\cutext{1/4}{cup}) cookie scoop, scoop a ball of dough onto a lined baking sheet. Using the back of your cookie scoop or your fingers, make an indent on the top of the dough. Sprinkle a couple tablespoons of the streusel on the top of the cookie, into the indent.
Bake the cookies at \cunum{350}{F} for \cutext{10--12}{min}. While they are baking, make the icing.