Possible Clues:

• As spelt perhaps, but its homonym would be a bloomer
• Ground cereal
• It's been through the mill
• In meal, two couples drink litre
• Finally full, having tucked into square meal
• Dusty white stuff left in number of suits?
• The sound of the blooming ground
• That's ground for 1 down, by the sound of it
• 4 about 50 for the ground
• About 50, 4 gets one of 15 across