Preheat oven to 335 degrees. Butter a 9-inch springform pan, line bottom with a round of parchment paper and butter parchment.
In the bowl of an electric stand mixer fitted with the paddle attachment (preferably one that scrapes bowl while mixing), whip together butter, sugar and dulce de leche on high speed until pale and fluffy.
Add in eggs and vanilla extract and blend on high speed until creamy, gently blend in milk (mixture may look curdled but it's fine).
In a medium mixing bowl whisk together flour, almond flour, baking powder and salt. Sift flour mixture over batter and gently fold just until combined.
Pour batter into prepared springform pan and smooth top. Bake in preheated oven for 30 - 35 minutes, the sides should be set but the center slightly under-baked.
Meanwhile prepare the caramel sauce.
In a heavy-bottomed 2-quart saucepan (something that isn't dark on bottom so you can see the shade of caramel), heat sugar and water over medium-high heat whisking constantly to dissolve sugar.
Once mixture reaches a boil, stop whisking and allow mixture to boil until it reaches a dark amber color, carefully swirling pan occasionally* (this will take time, so be patient).
It will first bubble vigorously and steam and it will be a clear shade, then bubbling will continue but the bubbles will become smaller and slower and it will slowly tint yellowish, then a medium shade of orange.
Once mixture reaches that orange color, immediately add butter and whisk until butter has melted then immediately remove from heat.
Carefully pour in cream and immediately whisk with a long handled whisk to combine (it will bubble vigorously). Whisk until mixture is smooth then pour into a bowl or jar so it doesn't continue to cook.
Remove cake after the 35 minutes then pierce all over with a chopstick. Slowly and evenly pour prepared caramel sauce over the cake (I reserved a few tablespoons to drizzle over the top before serving). Sprinkle with almonds.
Return cake to oven and bake until cooked through, about 10 minutes longer.
Remove from oven and let cake stand 10 minutes then run a knife around edges of cake to loosen and remove pan ring. Sprinkle with sea salt flakes, serve warm or cool completely and store in an airtight container.
Recipe source: adapted from The European Cake Cookbook, by Tatyana Nesteruk
*Note that if you are using a gas stove top I've found certain areas tend to cook faster on the gas stovetop, so if you start to see a darker area on the side you can give it a brisk whisking. Also using a wet pasty brush to wet down the dried sugar on the sides helps.