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!