Step 1

Place rack in lower third of oven; preheat to 325°. Lightly butter sides and bottom of a 9x5" loaf pan. Line pan lengthwise with parchment paper, leaving about a 2" overhang.

Step 2

Whisk flour, cinnamon, baking powder, nutmeg, baking soda, and cloves in a medium bowl to combine.

Step 3

Using an electric mixer on medium-high speed or a stand mixer fitted with the whisk attachment, beat sweet potato purée, oil, salt, and 1⅓ cups (266 g) sugar in a large bowl until well combined. Add eggs one at a time, beating well after each addition before adding the next. Scrape down sides of bowl with a rubber spatula. Add dry ingredients and beat until incorporated. Scrape down sides of bowl, then reduce speed to medium and continue to beat until smooth, 5–10 seconds (batter should be the consistency of a thick purée). Transfer batter to prepared pan; smooth surface with an offset spatula.

Step 4

Pour water to a depth of about 2" into a medium saucepan, heat over medium, and bring water to a simmer. Whisk egg whites and remaining ⅔ cup (134 g) sugar in a medium bowl (or use the stand mixer bowl) set over simmering water (do not let bowl touch water). Continue to whisk until whites are hot to the touch (an instant-read thermometer should register 120°), about 5 minutes.

Step 5

Carefully remove bowl from pan and immediately beat on high speed (or return bowl to stand mixer and beat with the whisk attachment) until mixture is very thick and holds stiff peaks when you lift out the beaters, 5–7 minutes. Add vanilla and beat to combine.

Step 6

Spoon meringue over batter. Drag a knife through meringue and batter to create a marbled pattern. Don’t thin out the meringue too much, though; it bakes best when left in thicker patches.

Step 7

Bake cake until a paring knife inserted into the center comes out clean, 90–100 minutes. Let cake cool in pan on a wire rack 20 minutes. Run a sharp knife around short sides of pan, lift out cake using parchment overhang, and let cool completely. Serve cake at room temperature.

Step 8

Do Ahead: Cake can be made 4 days ahead. Tightly wrap and store at room temperature, or chill up to 1 week.