If you search “favorite Chicago chocolate cake,” it’ll likely show Portillo’s as the top result. For good reason: It’s delicious. It’s also a secret recipe that Portillo’s won’t share. But Tony Rican of Bartlett, Illinois, tinkered with the recipe until he — with the help of a former Portillo’s manager — developed what he says is as close to the original as one can get. He spoke with Steve Alexander about the secret ingredients (it’s more than just mayonnaise) and how he became the Average Guy Gourmet. His Portillo’s knockoff recipe is below.

CAKE INGREDIENTS

1. 2 Cups Flour
2. 1/2 Cup Cocoa Powder
3. 1-1/4 tsp. Baking Soda
4. 1/2 teaspoon Baking Powder
5. 1 tsp. Instant Coffee
6. 1 tsp. Salt
7. 3 Eggs
8. 1 Cup Mayonnaise
9. 1 Cup Sugar
10. 1 1/4 cup Water
11. 1 tsp. Vanilla
12. 1/2 Cup Chocolate Chips (Optional)

CAKE PREP

1. Preheat the oven to 350F. Butter 2 round cake pans (9-inch ones) and line with parchment paper.
2. Mix together the flour, cocoa powder, baking soda, baking powder, coffee and salt in a bowl. Set aside.
3. Add the eggs, mayonnaise, sugar, water and vanilla into the flour mixture. Stir until well-blended but do not overmix.
4. Fold in the chocolate chips. Transfer the batter to the prepared pans.
5. Bake in the preheated oven for 20-23 minutes or until a toothpick inserted in the center comes out clean. Oven temperatures vary so adjust the time accordingly.
6. Cool the cakes in the pans for 10 minutes and then transfer to a wire rack. Cool the cakes completely before adding the chocolate filling and coating with the frosting.

FROSTING INGREDIENTS

1. 1 Cup Butter, softened
2. 1/2 Cup Cocoa Powder
3. 5 Cups Powdered Sugar
4. 1 tsp. Vanilla
5. 3 Tbsp. Milk (if needed to for consistency)

FROSTING PREP

1. Whip butter and cocoa together until smooth in large bowl. Stir in vanilla and powdered sugar. Slowly stream in milk until frosting reaches desired consistency. Scrape sides and whip again until light, fluffy and smooth, 1-2 minutes.