Preheat and prep the pan. Heat the oven to 375°F (190°C). Line a 12-cup muffin pan with paper liners or grease lightly.
Combine dry ingredients. In a large bowl, whisk all-purpose flour, almond flour, sugar, baking powder, and salt until evenly blended and lump-free.
Mix the wet ingredients. In a separate bowl or large measuring cup, whisk melted butter, milk, eggs, vanilla, and almond extract. If using lemon zest, add it here.
Bring the batter together. Pour the wet mixture into the dry ingredients. Stir gently with a spatula just until no dry streaks remain. The batter should be thick but scoopable. Do not overmix.
Fold in raspberries. Add the raspberries and fold them in with 3–4 light strokes. It’s fine if a few break; you want some whole pieces for bursts of flavor.
Fill the cups. Divide the batter evenly among the muffin cups, filling them almost to the top for a tall rise. Sprinkle with sliced almonds and coarse sugar, if using.
Bake. Bake for 18–22 minutes, until the tops are golden and a toothpick inserted in the center comes out mostly clean with a few moist crumbs. A bit of berry juice is normal.
Cool. Let the muffins rest in the pan for 5 minutes, then move them to a rack to cool. Enjoy warm or at room temperature.