Step 1
Place a rack in middle of oven; preheat to 350°. Place a piece of parchment paper on top of the base of springform pan. Place collar on top and close so it holds paper in place. Spray parchment and sides of pan with nonstick vegetable oil spray. Whisk 2 large eggs, room temperature, ⅔ cup buttermilk, room temperature, 2 Tbsp. vegetable oil, and 1 Tbsp. vanilla extract in a medium bowl to combine.
Step 2
Beat ½ cup (1 stick) unsalted butter, room temperature, 1⅔ cups (208 g) all-purpose flour, 1 cup plus 2 Tbsp. (225 g) granulated sugar, 1½ tsp. Diamond Crystal or ¾ tsp. Morton Kosher salt, 1½ tsp. baking powder, ¼ tsp. baking soda, and 1 tsp. finely grated lemon zest in the bowl of a stand mixer fitted with the paddle attachment, starting on low speed and gradually increasing to medium speed, until combined and fine crumbs form, 1–2 minutes. With the motor running, gradually stream in egg mixture and beat until no pockets of dry flour remain, about 1 minute.
Step 3
Scrape batter into prepared pan and smooth into an even layer. Arrange 2 large rhubarb stalks (about 8 oz.), trimmed, thinly sliced on a diagonal (about 3 cups), over batter in a single layer, slightly overlapping pieces. Sprinkle remaining 1 Tbsp. (13 g) granulated sugar on top. Bake cake until a tester inserted into the center comes out clean, 45–55 minutes. Transfer pan to a wire rack.
Step 4
Heat 3 Tbsp. strawberry jam, preferably seedless, in a small microwave-safe bowl in a microwave on high power just until liquefied and hot, 15–20 seconds. (Alternatively, heat in a small saucepan over medium.) If the jam is very seedy, pass through a fine-mesh sieve into another small bowl. Brush top of warm cake with jam, then sprinkle ¼ cup toasted sliced almonds around edges of top of cake if desired. Let cake cool in pan.
Step 5
Unmold cake and serve slices top with whipped cream or vanilla ice cream.