For the streusel:
Combine the flour, granulated sugar, brown sugar, almonds, cinnamon, and 1/2 teaspoon salt in the bowl of an electric mixture fitted with the paddle attachment. Mix just to combine. Add the butter and mix just until the streusel comes together. Spread onto a baking sheet and chill in the refrigerator until firm, about 1 hour.
Crumble the streusel with your fingers and store in an airtight container in the refrigerator or freezer until ready to use.
For the cake:
Preheat the oven to 350 degrees F. Line the bottom of an 8-inch cake pan with parchment paper. Butter the pan and the paper. Spread about 1 3/4 cups streusel around the bottom of the pan.
In a bowl, sift together the flour, baking powder, and salt; set aside.
Fill a medium saucepan with 2-inches water and bring to a simmer. In the bowl of an electric mixer, combine the eggs, granulated sugar, and lemon zest. Set the bowl over the saucepan of simmering water and whisk until the mixture is warm to the touch, about 2 minutes.
Transfer the bowl to an electric mixer fitted with the whisk attachment. Beat on medium speed until the mixture thickens, is a pale yellow, and forms ribbons when the whisk is lifted, 5 to 6 minutes.
Meanwhile, in another bowl, whisk together the oil, milk, and lemon juice. When the egg mixture has thickened, slowly drizzle in the oil mixture, with the machine running.
Reduce the speed to low, add the flour mixture, and mix just to combine. Drizzle in the butter and mix just to combine.
Pour the batter into the prepared pan over the streusel. Bake, rotating the pan once halfway through, until the top of the cake is golden, the center bounces back, and a cake tester inserted in the center comes out clean, about 50 to 60 minutes. Unmold the cake from the pan so that the streusel is on top and serve or cool completely on a wire rack. Once cool, wrap in plastic wrap.
NotesStreusel keeps, well sealed in an airtight container, in the refrigerator for up to 3 days or in the freezer for up to 1 month.