Banana Poppy Seed Muffins with Hazelnut Streusel

Adjust an oven rack to the lower middle position. Preheat the oven to 375F. Butter eight 3 x 2-inch soufflé molds and line the bottom of each mold with parchment paper. Place the molds on a baking sheet. (If using regular muffin tins, place liners in two standard 12-cup muffin tins. You want to fill the tins about 3/4 of the way full, and will get about 13-14 muffins. The baking time will be shorter.)

Whisk the flour, sugar, poppyseeds, baking powder, baking soda, and salt together in a large bowl. Make a well in the center.

In a large bowl or liquid measuring cup, whisk the mashed banana, sour cream, milk, butter, oil, egg, and vanilla until completely combined. Pour the wet ingredients into the well in the dry ingredients and mix gently until almost combined. Fold in the diced banana pieces until just incorporated, being careful not to overwork the batter (the batter should not be completely smooth; there should still be some visible lumps and bumps.)

Scoop the batter into the prepared molds. Sprinkle the tops generously with the hazelnut streusel (you may have some left over). Bake 15-20 minutes, until the edges are golden brown and a wooden skewer or toothpick inserted in the center comes out clean (if baking in regular muffin tins, the baking time will be shorter). Move the baking sheet to a wire rack to cool, and when the molds are cool enough to handle, carefully remove the muffins from each one.

In the bowl of a stand mixer, combine the all-purpose flour, sugars, hazelnut flour, salt, and cinnamon on low. With the mixer on low, add the butter, one tablespoon at a time, until the mixture comes together but still is quite crumbly. Streusel can be held in the refrigerator for 24 hours, or frozen for up to one month.