For the smoothest whipped feta, bring the cheese and cream cheese to room temperature at least 20 minutes before blending. Do not overmix the meatball mixture or they will become tough. Searing before roasting is essential for the best flavor and texture. The whipped feta and meatballs can be stored separately in the refrigerator for up to 3 days. Meatballs freeze well for up to 3 months — the whipped feta is best made fresh.