• Flash freeze your mulberries: place them in a single layer on a plate or baking sheet and pop in the freezer for 30-45 minutes. This helps keep the delicate berries from falling apart in your batter. You can do this just before you start your muffins, or days ahead of time. Just pack the frozen berries in a heavy duty zip lock freezer bag.
• Preheat oven to 375F and butter a muffin tin, or line with muffin tin liners.

the streusel

• Combine the ingredients with your fingertips until it is crumbly and the butter is completely incorporated. The mixture will be dry but keep at it until the moisture of the butter is thoroughly incorporated. Set aside.

the muffins

• In a large mixing bowl, whisk together the 2 large eggs, 1/2 cup vegetable oil, 3/4 cup granulated sugar, 3/4 cup buttermilk, and 2 tsp vanilla bean paste. Get everything well combined.
• Whisk in the 2 tsp baking powder, 1/2 tsp baking soda, and 1/2 tsp salt. Then fold in the 2 cups all purpose flour. When the flour is almost all incorporated, fold in the 1 1/2 cups mulberries.
• Fill your muffin cups quite full, and then sprinkle lightly with streusel mixture. Bake in a preheated oven for about 25-27 minutes, or until risen and just turning golden. Different ovens vary greatly, so check these on the early side.
• Cool slightly before turning the muffins out of the pan. Devour warm, with plenty of butter.