Peanut butter blossoms might turn out crumbly for a few reasons. Watch your time closely so they don't over bake, which can dry your cookie out. If your cookies have started to brown around the edges, you've gone too far. Make sure your oven is cooking at the correct temperature with an oven-safe thermometer. If the heat is too high, the cookies might end up dry and crumbly on the outside, and undercooked on the inside. Regular peanut butter works better than natural peanut butter for this recipe. Natural peanut butter may make your dough too dense.