Step 1

Place a rack in top third of oven; preheat to 375°. Now prep your peaches. These should be some of the sweetest, most fragrant peaches you can find. Better peaches make for a better peach crumble. (If you've got peaches that aren't ready, place them in a brown paper bag with a banana, then check back every day. The banana will speed up the ripening process.) Slice 2½ lb. peaches (6–in half with a chef’s knife. Using a paring knife, cut around pits; pry them out if necessary ("clingstone" peaches have pits that cling to the flesh, whereas "freestone" peaches' pits can be easily pried out). Cut each peach half in half (so you have peach quarters), then cut each quarter into half twice more (you want 4 thin slices from each quarter, or 16 thin slices from each peach). As you go, transfer peach slices to a 13x9" baking dish.

Step 2

Zest 1 lemon into a medium bowl; set aside.

Step 3

Sprinkle ⅓ cup sugar, 1 Tbsp. fresh lemon juice (from the zested lemon), and ¾ tsp. salt over peaches. Toss to gently combine, then let sit while you prep the topping—aim for about 20 minutes. The maceration draws the sugar out of the fruit, making the peaches taste even peachy-er.

Step 4

Spread ⅓ cup raw white sesame seeds on a rimmed baking sheet or in an ovenproof skillet. Toast, tossing halfway through, until golden brown all over, 12–15 minutes. Toasting the sesame seeds yourself makes for a deep, nutty richness that store-bought toasted sesame seeds cannot match. Immediately transfer to a large bowl (so they don’t keep cooking on hot baking sheet).

Step 5

Add 1 cup all-purpose flour and remaining 1¼ cups sugar and 1 tsp. salt to bowl with seeds. Whisk to combine.

Step 6

Add ½ cup (1 stick) butter and ½ tsp. ground cinnamon to medium bowl with lemon zest. Microwave until butter is melted, about 1 minute. Add ⅓ cup tahini and 2 tsp. toasted sesame oil and whisk to combine.

Step 7

Pour tahini-butter mixture into dry ingredients, then mix until dry ingredients are incorporated and mixture holds together when you squeeze it in your hands.

Step 8

Assemble! The peaches should look juicy. And now you determine whether you’re using 1 tsp. (or more) cornstarch. If peaches are not-so-ripe, skip it entirely. If they’re perfectly ripe, use 1 tsp. And if they’re really juicy, use 2 tsp. Gently toss to combine.

Step 9

Using your hands, squeeze crumble topping into big hunks, then break off uneven pieces and scatter over peaches.

Step 10

Bake crumble until topping is well browned and firm and peaches are tender with bubbling juices, 60–70 minutes.

Step 11

Serve warm with vanilla ice cream (if using).