Step 1: Gather all your ingredients (mixed berries, Greek yogurt, honey/maple syrup, lemon juice, vanilla extract) and equipment (blender, popsicle molds, sticks).
Step 2: Place the mixed berries (fresh or frozen) and fresh lemon juice into your blender. Blend until you achieve a smooth puree. For a super smooth texture, strain the puree through a fine-mesh sieve to remove seeds.
Step 3: Add the plain Greek yogurt, honey or maple syrup, and vanilla extract to the berry puree in the blender. Blend again until the mixture is completely smooth and well combined. Taste and adjust sweetness as desired, remembering that frozen items taste less sweet.
Step 4: Carefully pour the berry yogurt mixture into your popsicle molds, filling them almost to the top, leaving a small space for expansion.
Step 5: If your molds have lids with built-in stick holders, place them on. Otherwise, once the popsicles have frozen for about 30-60 minutes (enough for them to be slightly firm but not completely solid), insert the popsicle sticks straight into the center.
Step 6: Place the filled molds in the freezer on a level surface and freeze for at least 4 hours, or preferably overnight, until completely solid.
Step 7: To unmold, run the molds under warm water for 10-20 seconds. Gently twist and pull to release the popsicles. Serve immediately or store in an airtight container in the freezer.