Preheat oven to 350oF. Butter three round 8-inch cake pans, line the bottoms with parchment, then butter the parchment. Flour the pans; set aside.
With an electric mixer, cream together the butter and oil until fully blended. Add in the sugar, strawberry gelatin and baking powder. Beat several minutes on medium speed until combined and fluffy.
Add in the eggs one at a time, beating well after each addition. Scrape down the bottom and sides of the bowl as needed.
In a large measuring cup, combine the strawberry purée, milk and vanilla.
Add in the flour in three additions, alternating with the liquid mixture. Begin and end with the flour, adding the salt with the last addition. Beat just until incorporated.
Pour the batter evenly into the prepared cake pans, smoothing the tops with an offset spatula.
Bake the cakes for 25-35 minutes, or until a toothpick inserted into the center comes out clean, or with a few loose crumbs.
Cool in the pans on a cooling rack for 10 minutes. Remove the cakes from the pans, peel off the parchment paper, and then set right-side up on the cooling rack to cool completely.
For the frosting, place the egg whites and sugar in a bowl of a stand mixer. Place the bowl over a pan of simmering water, not touching the water. Whisk constantly until the sugar is dissolved and the mixture comes to a temperature of approximately 160F.
Immediately place the bowl on the stand mixer and whip on high using the whisk attachment until the frosting has become thick and glossy, forming a stiff peak. Continue to whip the frosting until the bowl feels room temperature to the touch or a total of about 10 minutes.
Switch the whisk attachment to the paddle attachment. With the mixer on low, drop in the butter, one tablespoon at a time, beating until smooth after each addition. If the frosting appears curdled or clumpy at any time, increase the speed to medium-high and beat until smooth.
Once all of the butter has been incorporated, mix in the amaretto and pinch of salt.
To assemble, spread about 2/3 cup frosting in between each layer of cake. Use the remainder to cover the sides and top of the cake with an offset spatula.
Store in the refrigerator.