Magic Cappuccino Cake or Smart Pie

Ingredients:

• 6 tbsp (90 g) butter
• 3 large eggs, room temperature, separate the yolks from the whites
• 3/4 cup granulated sugar
• 0.5 cups flour
• 1 tsp ground cinnamon + extra for serving
• 1/8 tsp fine salt
• 1.5 cups of milk
• 5 tsp dry instant espresso coffee
• 1 tsp vanilla extract
• 0.5 tsp cream of tartar
• Powdered sugar for serving
• Whipped cream for serving

Preparation:

1. Position a rack in the middle of the oven and preheat the oven to 325°F (160°C). Line a 20cm square metal baking pan with a 30cm x 20cm piece of parchment paper, allowing the ends to hang over both sides.
2. In a small microwave-safe bowl, melt the butter in the microwave for 1 minute. Brush the parchment paper with the melted butter, then invert it and press it into the pan. Brush the other side of the paper and the sides of the pan with butter.
3. Vigorously whisk the egg yolks and sugar in a large bowl until pale, creamy, and thick, 1-2 minutes. Pour in the remaining melted butter and whisk to combine. Add the flour, cinnamon, and salt and knead into a dough.
4. Pour the milk into a microwave-safe bowl or measuring cup and microwave for 1 minute until warm. Stir in the coffee and vanilla extract, whisking until completely dissolved. Slowly pour the milk mixture into the batter, whisking constantly until fully combined (the batter will be runny).
5. In a clean bowl, beat the egg whites and cream of tartar with a mixer on medium speed until stiff peaks form, about 2 minutes. Fold the beaten whites into the batter, lightly whisking them. Using a whisk, gently fold the batter several times to coat the whites with liquid while maintaining as much volume as possible (the batter will not be smooth). Pour the batter into the prepared pan and gently smooth the top with a rubber spatula.
6. Bake until the top of the pie is golden brown and puffed, about 1 hour. The pie should be set but still slightly jiggly in the center. Cool completely in the pan, about 2 hours.
7. Before serving, dust the top of the pie with powdered sugar and a little cinnamon. Run a small offset spatula or thin knife between the pie and the sides of the pan. Pull the overhanging ends of the parchment paper to lift the pie and transfer it from the pan to a cutting board. Cut the pie into 9 squares and serve with whipped cream.