In a small saucepan, add the frozen peas, diced potato, and garlic clove. Cover with just enough water to submerge the vegetables.: When you first tip the frozen peas into the saucepan you'll notice their deep green color and a cold, slightly crunchy texture. As you add the small, finely diced potato and lone garlic clove, aim to pour only enough water to just cover them so the flavors stay concentrated. This small volume allows the heat to transfer quickly, so the pot will come to temperature evenly. If you overfill the pot, the cooking liquid will dilute the vegetal sweetness and lengthen cooking time. A frequent slip is adding too much water, which results in a blander mash; the remedy is saving a little of the cooking water aside, rather than using excess at the start.
Bring to a boil, then reduce to a simmer. Cook for 10–12 minutes, or until the potato is fork-tender. Drain the water (reserving a little if you want to thin the mash later).: You'll hear the pot move from quiet to a lively simmer, punctuated with gentle bubbling as the potato softens. The aroma will shift from raw starch to a faintly sweet, verdant note from the peas . Using a fork to test the potato is the best cue, it should slide through without resistance. Drain carefully but keep a small amount of the starchy cooking liquid in a measuring cup if you think you might loosen the mash later. A common mistake is undercooking the potato, leaving gritty texture, so always test a piece before draining.
Add butter and olive oil to the warm veg and mash until smooth or slightly chunky, depending on your little one’s texture preference. Add a splash of water or milk to loosen if needed.: As you add the butter and olive oil to the hot vegetables, they will melt and begin to coat each piece, creating a glossy sheen. The scent will turn richer, and the mash will take on a silky mouthfeel. Use a potato masher or fork and work with patient, rhythmic pressure to achieve the texture you want. Start with gentle mashes for a chunky result or more vigorous mashing for silkier purée. If the mixture feels too stiff, add a tablespoon of the reserved cooking water or a splash of cream to loosen it. A misstep here is overworking the mash which can become gluey if the potato is too broken down, so stop when you reach the texture you like.
Let it cool slightly before serving to babies. Store leftovers in an airtight container in the fridge for up to 2 days, or freeze in portions for later.: Cooling reveals the final texture and ensures it is safe for small mouths, the warmth settling into a comforting fragrance rather than scalding. When cooled, the mash firms slightly, so check the texture before serving to infants, and adjust with a little reserved cooking water if needed. Transfer leftovers into airtight containers to preserve color and flavor, and label frozen portions for convenience. A common oversight is placing hot food directly into the fridge which can raise temperatures; allow the mash to come closer to room temperature before refrigerating to maintain food safety and quality.