Preheat the oven to 350℉/170℃ Fan. Line an 8" circular pan with parchment/baking paper.
In a large bowl/bowl of a stand mixer, add all the cake ingredients and combine until smooth. If very stiff, add a little more milk.
Pour into the lined pan and bake for 30-35 minutes.
While that's baking, make the frangipane: Combine the ground almonds, butter, egg, sugar, milk and almond extract (optional) to form a paste. Do this either with a spatula or with an electric mixer.
Once the cake has baked 30-35 minutes, spread this frangipane mix over the top, scatter over the slivered almonds and bake a further 10 minutes.
Remove and let cool before dusting with powdered sugar and serving!