Step 1

Place a rack in middle of oven; preheat to 350°. Coat Bundt pan with nonstick spray, then lightly dust with flour, tapping out excess.

Step 2

Beat brown sugar, baking powder, cinnamon, salt, baking soda, and 2 cups flour in the large bowl of a stand mixer fitted with the paddle attachment on low speed until combined (or use a hand mixer and large bowl). Add butter (make sure it’s at room temperature) and beat on medium-low speed until mixture resembles coarse sand. Add sour cream and vanilla and continue to beat, increasing speed from medium-low to medium as the ingredients begin to incorporate, until batter is thick and smooth, about 1 minute. Scrape down sides of bowl. Reduce mixer speed to medium-low, add 1 egg, then increase speed to medium and beat 30 seconds. Repeat with remaining 2 eggs, reducing speed to medium-low after each addition, then increasing speed to medium-high and beating for 30 seconds (if you beat on medium-high speed from the get-go, you risk losing some of the batter; this ensures nothing flies out of the bowl). Scrape down sides of bowl again. Reduce speed to low, add dates, and beat until incorporated, about 30 seconds longer.

Step 3

Scrape batter into prepared pan; smooth surface. Bake cake until a tester inserted into the center comes out clean and cake springs back slightly when pressed, 40–50 minutes. Let cool at least 20 minutes in pan, then turn out cake onto a platter and let cool completely.

Step 4

Do Ahead: Cake can be made 1 day ahead. Let cool, then cover with plastic wrap. Store at room temperature.

Step 5

Melt brown sugar and butter in a small saucepan over medium-low heat, whisking constantly, until mixture is thick and smooth and brown sugar is dissolved, 4–6 minutes. Remove pot from heat and whisk in vanilla, ¾ cup sour cream, and 1½ tsp. sea salt until smooth.

Step 6

Arrange torn dates in a ring on top of cake. Drizzle ½ cup sauce over cake and dates. Sprinkle with more sea salt. Serve cake with sour cream and remaining toffee sauce alongside. If the sauce has cooled and tightened up, gently reheat in saucepan over medium-low just until warm.