Preheat your oven to 425 degrees. Line a large rimmed baking sheet with parchment paper or foil. A hot oven is key here because you want the cut sides to caramelize, not steam.

Trim the ends off each delicata squash, then cut them crosswise into rings about 3/4 inch thick. Use a spoon to scoop the seeds and stringy bits out of each ring. The skin is thin and edible so there is nothing to peel.

In a large bowl, toss the squash rings with the olive oil, kosher salt, and black pepper until every piece is coated. Spread them in a single layer on the prepared baking sheet. Do not stack them. If they overlap, they will steam instead of roast and you will miss the caramelization.

Roast for 12 minutes, then flip each ring with a spatula or tongs. The underside should already look golden and starting to brown. Roast for another 10 to 13 minutes until both sides are deep golden and the squash is tender when you pierce it with a fork. The edges should look slightly darker than the center.

While the squash finishes roasting, make the brown butter. In a small light-colored saucepan over medium heat, melt the butter. Once it is melted and foamy, add the sage leaves. Cook, swirling the pan often, for 2 to 3 minutes. The butter will turn from pale yellow to golden to a warm amber color and smell like toasted nuts. The sage leaves will crisp up and darken. The moment you see the butter turn amber and smell nutty, pull it off the heat. It can go from brown to burnt in under a minute.

Remove the pan from heat and stir in the maple syrup. It will bubble up briefly. Stir to combine.

Arrange the roasted squash rings on a serving platter. Spoon the brown butter and crisped sage leaves over the top. Scatter with flaky sea salt. Serve right away while the squash is hot and the butter is still glossy.