My cake is moist but crumbly I have always used this recipe and this turns out really soft and moist, but also crumbly. How can I fix it?
Here are the ingredients:

1 1/2 cups (3 sticks) unsalted butter, room temperature, plus more for pans

3/4 cup Dutch-process cocoa powder, sifted, plus more for pans

3/4 cup hot water

3/4 cup sour cream

3 cups cake flour, (not self-rising), sifted

1 teaspoon baking soda

1/2 teaspoon salt

2 1/4 cups sugar

4 large eggs

1 tablespoon pure vanilla extract


I haven't used up all the batter yet, so I can do changes if required. Please help!
Replacing part of the water and/or cream with more egg should do the trick, as when eggs are headed, they firm up and act as a binding element, fixing the crumblyness of your cake.