Peel and slice 3 of the peaches into 1/2-inch wedges, then add them to a food processor with 3/4 cup sugar. Blend until completely smooth, about 1-2 minutes. I find that using ripe peaches with good color ensures the most vibrant, naturally sweet flavor without needing extra sugar. Set the puree aside in a large bowl.

Add the Greek yogurt, vanilla essence, lemon juice, and fleur de sel to the peach puree. Whisk together until smooth and fully combined, making sure there are no lumps of yogurt remaining. The lemon juice brightens the peach flavor without being detectable as citrus, so don't skip it. This mixture is now ready to churn.

While the yogurt mixture is being prepared, peel and dice the remaining peach into small 1/4-inch pieces. The smaller dice will distribute better through the frozen yogurt during the final moments of churning and create pleasant texture pockets throughout. Set aside in a small bowl.

Pour the yogurt mixture from Step 2 into your ice cream maker and churn according to the manufacturer's instructions, typically 20-25 minutes. About 5 minutes before the churning cycle ends, add the diced peach from Step 3 and let it incorporate throughout the remaining churn time. This timing ensures the peach pieces stay distinct rather than breaking down into the mixture.

Transfer the churned frozen yogurt to a serving dish. Serve immediately for a soft-serve consistency, or place in the freezer for 10-15 minutes if you prefer a firmer scoop. I like to dust with a tiny pinch of fleur de sel just before serving to enhance the peach flavor and add a subtle sophistication.