1. Prepare the Oven and Dry Ingredients:

Preheat the oven to 350°F (175°C).

Combine the cake flour and salt in a medium bowl.

Sift together five times. This helps to aerate the flour and ensure a light and airy cake. Set aside.

2. Whip Egg Whites: In the clean, dry bowl of a stand mixer (or using a hand mixer and a large, clean, dry bowl), beat the room-temperature egg whites until frothy (lots of bubbles but still liquidy and loose).

Add the cream of tartar.

Continue to beat on high speed until stiff peaks form. The peaks should stand straight up when the beaters are lifted.

3. Gradually Add Sugar:

With the mixer on medium-low speed, slowly sprinkle in the sifted sugar, a little at a time, as it mixes in.

4. Fold in Flour: Remove the bowl from the mixer.

Gently fold in the sifted flour mixture, a little at a time, using a rubber spatula. Be careful not to overmix, as this can deflate the egg whites.

Sprinkle the vanilla extract into the bowl.

Fold gently to combine.

5. Pour Batter into Pan: Spoon the batter into an ungreased 10-inch tube pan (with a removable bottom).

Smooth the top of the batter with a spatula.

6. Bake:

Bake for 35-45 minutes, or until a wooden skewer inserted all the way to the bottom comes out clean. Do not open the oven while the cake is baking, as this can cause it to collapse.

7. Invert and Cool: Carefully remove the cake from the oven.

Immediately invert the pan onto a wine or vinegar bottle (or any object that will allow the cake to hang upside down without touching the counter).

Let the cake cool completely while hanging upside down. This prevents it from collapsing.

8. Remove from Pan: Once the cake is completely cool, carefully remove it from the pan. Run a thin knife or spatula around the edges of the pan.

9. Make the Filling:

While the cake is cooling, make the filling.

Sprinkle the strawberry Jell-O powder into a bowl.

Pour in 2 ½ cups of boiling water.

Stir to dissolve the Jell-O completely.

Add the bag of frozen sliced strawberries.

Stir to cool the mixture.

Set the mixture aside to cool and thicken.

IMPORTANT: If the mixture is not thick and gelatinous, place it in the freezer for 15 minutes, or until it thickens and sets to a spoonable consistency.

10. Prepare the Cake for Filling:

Turn the cooled cake upside down so that the end that was stuck to the bottom of the pan is now facing up.

With a serrated knife, carefully cut the top 1 inch of cake from the top. Remove this layer and set it aside.

Next, with a small paring knife, make two concentric cuts in the cake: one cut is 1 inch from the outside rim, the other cut is 1 inch from the inside rim. Be careful not to cut all the way through to the bottom of the cake! Leave about an inch from the bottom.

Tear out a trench in between the two cuts, creating a hollow space for the filling. Save the torn cake pieces for another use (cake pops, trifles, etc.).

11. Fill the Cake:

Carefully spoon the cooled and thickened strawberry mixture into the trench in the cake. Filling it all the way to the top and even slightly above, to allow for a little settling.

Place the top layer of cake back on top, lining it up carefully.

12. Chill: Refrigerate the cake for a couple of hours (or you can stick it in the freezer for an hour or so if you’re in a hurry!).

13. Make the Whipped Cream: To serve, whip together the heavy cream and sugar until stiff peaks form.

14. Frost and Serve:

Spread the whipped cream all over the cake, covering the top and sides.

Cut into slices and serve! Note that once you make a cut, the filling will slightly seep out of the remaining cake, but not overly so. Enjoy your beautiful and delicious Strawberry Angel Food Cake!