Put the flour, sugar and salt in a food processor and pulse briefly to combine. Add the butter and cream cheese and pulse until the butter and cream cheese pieces are slightly larger than pea size, about 10 to 12 pulses depending on your machine. Drizzle the water and lemon juice evenly over the flour mixture. Pulse until the dough begins to form moist crumbs that are just beginning to clump together, about 8 or 9 more pulses depending on your machine.

Dump the moist crumbs onto a workspace and gather into a pile. With the heel of you hand, push and gently smear the dough away from you until the crumbs come together. Two or three ‘smears’ should do the trick. Shape into a 5-inch disc and wrap tightly in the plastic wrap and refrigerate for 30 minutes, or up to 2 days.

Put the oats, ground flax seed, flour, salt, brown sugar, cocoa nibs, cinnamon, and cardamom in a small bowl and stir until well blended.

Add the butter and, using a fork (or your fingers), mix and mash until the ingredients are well blended and form small crumbs. Pop in the fridge while you make the filling and assemble the tarts.

Position an oven rack in the lower third of the oven and heat the oven to 375°F. Abby recommends lightly greasing the muffin cups, but I didn't find it necessary - probably because I was using such small muffin molds. If you opt for regular sized muffin molds, I'd follow her direction on this.

Set the wrapped, chilled dough on the counter at room temperature until it’s pliable enough to roll, only a few minutes at the most. Arrange a large piece of plastic wrap or parchment on the work surface and put the dough in the center. Cover with another piece of plastic or parchment and press down on the dough to flatten. Using a rolling pin, roll the dough between the plastic or parchment to about ⅛- inch thickness, turning, lifting and repositioning the plastic or parchment and lightly flouring throughout the rolling. Using a cookie cutter a little larger than the muffin molds, cut out rounds. Gather up the scraps, reroll to a ⅛-inch thickness, and cut another round. Repeat until the dough is all used. I ended up being able to make 24 rounds.

Working with one round at a time, use your fingers to gently press the dough into a prepared muffin cup, making sure there are no air bubbles in the bottom and the dough is pressed firmly and evenly up the side to the top of each cup. Repeat with the remaining dough rounds. If your kitchen is hot, slide the muffin tins into the frig while you make the filling.

Put the sugar, flour, and salt in a medium bowl and, using a table fork, mix until well blended. Add ½ cup each of the blueberries and blackberries, and using the table fork, slightly crush the berries while stirring them into the sugar-flour mixture. Add the remaining berries and the cream cheese and coconut milk and toss to coat evenly.

Evenly spoon the filling into the lined muffin cups (they will be completely full). Scatter the streusel evenly over the filling – don’t be shy.

Bake until the crusts and streusel are golden brown and the filling is bubbling, 27 to 29 minutes. Move the muffin tin to a wire rack. Using a paring knife, run the blade between the crust and the pan to loosen the tarts from any sticky berry juices and let cool for 10 minutes. Using a thin, metal spatula or the paring knife, carefully remove the tarts from the muffin cups and set them on a wire rack. Serve warm or at room temperature.