Preheat oven to 350 degrees. Add 4 eggs, condensed milk, and milk to blender. Blend well. Set Aside
Spray pan with cooking oil. (I recommend using a Bundt Pan as it helps distribute heat more evenly.)
Pour Dulce de Leche into greased pan, enough to cover the bottom of the pan but also leaving some aside for garnishing.
Pour the Flan Mixture from the blender into the pan. Set Aside.
Blend cake mix, water, oil, and 3 eggs in large bowl at low speed until moistened (about 30 seconds). Beat at medium speed for 2 minutes.
Pour Cake batter into pan. Making sure to evenly distribute it all around. (Flan and Cake Mixture will seem as if they are mixed, this is fine. During baking, chemistry will work its magic and ensure the two batters are unmixed.)
Place cake in center rack of the oven and bake for 35 min.
Cake is done when toothpick inserted in center comes out clean.
Once cake is done, remove from oven. Cool in pan on wire rack for 15 minutes. Invert the cake on a plate. Drizzle Dulce de Leche on top and sprinkle with sliced almonds. Serve.