Add water, sterilize, and pour!
Malt extract agar (MEA) is a highly versatile culture medium for fungi. Most mycelia find it nutritious and delicious.
Shake well before use and store in a cool, dry place. Malt extract is highly hygroscopic and will readily absorb moisture from the air.
Use 30g for every 750mL of (preferably distilled) hot water, whisk to dissolve, sterilize at 15psi for 45 minutes, and pour your petri dishes! This recipe will conveniently produce ~25 dishes. Seal your dishes with Parafilm or micropore tape after setting.