Preheat oven to 375° F. Position the oven rack in the upper third of the oven. Line 12 muffin cups with paper liners. Line a baking sheet with parchment paper.
In the bowl of an electric mixer, blend the sugar and almond paste together well, about 2 to 4 minutes. Add the ground almonds, butter, and oil and blend well. Fold in the flour, baking powder, baking soda, salt, and poppy seeds and blend, scraping the bottom of the bowl occasionally to ensure nothing gets stuck in the well of the mixing bowl. If the mixture seems too loose, add a touch more flour. It should be the consistency of thick cake batter.
Scoop the batter into the prepared muffin cups. Top each muffin with some slivered almonds and sugar. Place the muffin cups on the prepared baking sheet.
Bake about 30 to 35 minutes, until the muffins are nicely browned and spring back when lightly touched. Let them cool in the pan for 15 minutes before turning them out onto a rack to cool completely.
Recipe by Not Just Sunday Dinner at https://notjustsundaydinner.com/almond-poppy-seed-muffins/