Preheat oven to 325 degrees F. Lightly grease (or spray with nonstick spray) a jelly-roll pan that is 15x10 inches.
In a large bowl, whisk together flour, granulated sugar, baking soda, cinnamon, ancho chili powder, and salt until well combined.
Stir in sour cream, eggs, and 1 teaspoon vanilla until just combined.
Meanwhile, melt 1 cup butter in a small saucepan over medium-high heat. Stir in water and 1/4 cup cocoa and bring to a boil stirring constantly until smooth. Cool slightly then stir into cake batter.
Pour cake batter into prepared pan and cook about 20-25 minutes or until toothpick comes out clean.
When cake is almost done, start preparing icing by melting 1/4 cup butter in small pan over medium-high heat. Stir in milk, cajeta, and 1/4 cup cocoa powder. Bring to a boil while stirring constantly. Slowly stir in powdered sugar and continue stirring until smooth. Stir in 1 teaspoon vanilla. Cool slightly but keep warm.
Pour icing over warm cake (be careful that frosting does not go over edge of pan). Cool cake in fridge or on wire rack for frosting to set.
SNAPPY TIPS: If you’re unsure about using cinnamon and/or ancho chili pepper, add it at the end and add just a little at a time. Depending on the size of the sides of your pan you may have frosting leftover. Use it to top ice cream or after frosting has set on cake, add more icing on to the cake then cool again in fridge or on wire rack.SNAPPY SUBSTITUTIONS: You can use any store bought or homemade cajeta, dulce de leche, or thick caramel. Any kind of nut could be substituted for the almonds, or omit. Regular unsweetened cocoa powder could be used instead of the dark.