• Preheat your baking oven to 350°F (180°C). Grease an 8-inch pan and line it with parchment paper.

Crust

• Mix the butter and granulated sugar in a mixing bowl until combined. Crack in the egg with a splash of vanilla and beat again.
• Add flour, baking powder, and salt while the mixer is at low speed. Keep mixing until thick and crumbly, then switch to a rubber spatula and give it a final mix.
• Press the dough down onto the pan's sides and bottom until it's roughly 1.5 inches (or 4 cm) high. Sprinkle on extra flour if it starts getting sticky.
• Refrigerate during the next steps

Streusel Topping

• Toss all-purpose flour, brown sugar, a pinch of salt, and a generous dash of cinnamon in a bowl. Whisk until combined.
• Mash the butter into the mixture with a small fork until crumbly. Sprinkle in flaked almonds.
• Set it aside.

Apple Filling

• Peel the apples, then core them and slice them up. Chuck the slices into a bowl, add lemon juice and cinnamon. Toss until they're all coated.
• Fill the cake crust with apple slices and top with almond streusel.

Baking & Serving

• Bake for 40 to 45 minutes. If the streusel starts getting too toasty, throw aluminum foil over the top and keep baking.
• Let it cool in the baking pan for a few minutes, then dust with a teaspoon or two of powdered sugar and serve. You can go with any pairings you like.