Prep the pan and oven: Heat oven to 350°F (175°C). Grease an 8-inch round cake pan (or line with parchment) so the cake releases cleanly.
Mix dry ingredients: In a large bowl, whisk almond flour, protein powder, sweetener, baking powder, baking soda, and salt until evenly combined.
Whisk wet ingredients: In a separate bowl, whisk eggs, Greek yogurt, almond milk, oil, vanilla, and almond extract until smooth.
Combine: Pour wet ingredients into dry.
Stir gently with a spatula until just combined. The batter should be thick but scoopable. If it’s too thick, add 1–2 teaspoons more milk.
Pan and top: Spread the batter evenly into the pan.
Smooth the top and sprinkle with sliced almonds if using.
Bake: Bake for 22–28 minutes, until the top is lightly golden and a toothpick comes out mostly clean with a few moist crumbs.
Cool: Let the cake cool in the pan for 10 minutes, then transfer to a rack to cool at least another 20 minutes before slicing. This helps set the crumb.
Serve: Enjoy plain, dust with a little powdered sweetener, or add a spoonful of Greek yogurt and fresh berries.