Why is my cake crumbly? I used a new cupcake recipe. It has raving reviews about how moist it is. Mine turned out moist but it's very crumbly. Any suggestions?

Ingredients


1 1/2 cups semisweet chocolate morsels
1/2 cup butter, softened
1 (16-oz.) package light brown sugar
3 large eggs
2 cups all-purpose flour
1 teaspoon baking soda
1/2 teaspoon salt
1 (8-oz.) container sour cream
1 cup hot water
2 teaspoons vanilla extract


Directions


Beat butter and sugar at medium speed with an electric mixer until well blended (about 5 minutes). 
Add eggs, 1 at a time, beating just until blended after each addition. Add melted chocolate; beat until blended.
Sift together flour, baking soda, and salt. Gradually add to chocolate mixture alternately with sour cream, beginning and ending with flour mixture. Beat at low speed just until blended after each addition. 
Gradually add hot water in a slow, steady stream, beating at low speed just until blended. Stir in vanilla.
This looks very similar to a recipe that I make for chocolate cake. Mine was always a bit crumbly until I changed my measuring technique for the flour. Instead of scooping and leveling I spooned the flour in to the cup and then I leveled it. That made a huge difference. Of course, weighing is even better. 

It could also be an issue of slightly over baking. You could try testing them 5 minutes earlier. 

Those two things tend to be the crumbly culprits in cake.